Fixes for new machine install

Summary:
While re-installing onto a brand new install, I ran into several issues and noticed some things that are no longer needed. Specifically:
* Installing `yarn` via homebrew has the potential to overwrite the `node` we have installed (usually with a newer version than we want). Instead, it's easiest to just use `npm` to install yarn globally.
* `readline` is a [[ https://khanacademy.slack.com/archives/C02NMB1R5/p1606758044205900 | perenial ]] [[ https://khanacademy.slack.com/archives/C02NMB1R5/p1601497407132100 | problem ]] to get installed with `pip`. But our version of Python comes with `readline` packaged into it, and that version of readline properly switches between readline and libedit (macOS) depending on the OS it's on. I don't think we need to install the readline module manually any longer (see https://pypi.org/project/gnureadline/)
* Don't force-install [email protected] - that breaks `make install_deps` in webapp

Issue: "none"

Test Plan: Well, I guess the best way would be to run this diff on a fresh install of macOS.

Reviewers: ebrown, csilvers, benkraft

Reviewed By: ebrown

Subscribers: bryan, john, kevinb, jeff, csilvers

Differential Revision: https://phabricator.khanacademy.org/D68282

mac-setup.sh

@@ -302,11 +302,6 @@ install_node() {
         notice "\t${tty_bold}brew link --force --overwrite node@12${tty_normal}"
         read -p "Press enter to continue..."
     fi
-    if ! which yarn >/dev/null 2>&1; then
-        # Using brew to install node 10 seems to prevent npm from
-        # correctly installing yarn. Use brew instead
-        brew install yarn
-    fi
 }
 
 install_go() {
@@ -342,9 +337,9 @@ install_postgresql() {
     if [ "$pg11_brewname" = "NONE" ] ; then
         info "Installing postgresql\n"
         brew install postgresql@11
-        # swtich icu4c to 64.2
-        # if default verison is 63.x and v64.2 was installed by postgres@11
-        if [ "$(brew ls icu4c --versions |grep "icu4c 63")" ] && \
+        # switch icu4c to 64.2
+        # if default version is 63.x and v64.2 was installed by postgres@11
+        if [ "$(brew ls icu4c --versions | grep "icu4c 63")" ] && \
            [ "$(brew ls icu4c | grep 64.2 >/dev/null 2>&1)" ]; then
            brew switch icu4c 64.2
         fi

setup.sh

@@ -254,16 +254,9 @@ install_deps() {
 
     create_and_activate_virtualenv "$ROOT/.virtualenv/khan27"
 
-    # Inspiration from this slack discussion
-    # https://khanacademy.slack.com/archives/C0918TZ5G/p1560899833202100
-    # In general, need to pin npm to V6.4.1
-    # Also, need to install yarn first before run `make install_deps`
+    # Need to install yarn first before run `make install_deps`
     # in webapp.
-    # TODO(avidal): Is this still necessary? That's an ancient version of npm
-    # and you can get yarn via brew or via your distribution.
-    if ! which yarn >/dev/null; then
-        echo "Installing yarn"
-        sudo npm install -g [email protected]
+    if ! which yarn >/dev/null 2>&1; then
         sudo npm install -g yarn
     fi
 

shared-functions.sh

@@ -152,8 +152,7 @@ has_recent_go() {
 
 # Creates a webapp virtualenv in $1, if none exists, then activates it.
 #
-# Assumes pip and virtualenv are already installed.  Note this also
-# pre-installs the correct readline on OS X -- see comments below.
+# Assumes pip and virtualenv are already installed.
 #
 # Arguments:
 #   $1: directory in which to put the virtualenv, typically ~/.virtualenv/khan27.
@@ -164,20 +163,6 @@ create_and_activate_virtualenv() {
 
     # Activate the virtualenv.
     . "$1/bin/activate"
-
-    # On OSX 10.15, we need to install an older version of readline
-    #  so that when pip will not install the latest, which results
-    #  in a library error trying to load readline/libreadline.a
-    # This must be done after installing the virtualenv.
-    if [ "`uname -s`" == "Darwin" ] && sw_vers -productVersion | grep -q -e '^10\.15\.'; then
-        echo "On OSX 10.15 - Installing readline 6.2.0"
-        if [ -z "$(pip --disable-pip-version-check freeze | grep readline)" ] ; then
-            # Long deprecated library - clang generates many warnings which
-            # cause build to fail. We add a -w here to disable *all* warnings.
-            # It is the only way found to get the install to work.
-            CFLAGS='-w' pip install https://pypi.python.org/packages/source/r/readline/readline-6.2.0.tar.gz
-        fi
-    fi
 }
 
 # If we exit unexpectedly, log this warning.