build: Remove workaround for -F in Qt linker flags on macOS.

* m4/acinclude.m4 (OCTAVE_CHECK_QT_VERSION): It doesn't seem to be necessary
to link all dependencies with Qt on macOS any longer. Remove work-around that
dates back to January 2014.
* configure.ac (link-all-dependencies): Adjust documentation.

configure.ac

@@ -690,7 +690,7 @@ case $host_os in
 esac
 AC_ARG_ENABLE([link-all-dependencies],
   [AS_HELP_STRING([--enable-link-all-dependencies],
-    [link Octave and its shared libraries with all dependencies, not just those immediately referenced (should not be needed on most systems).  This is done by default for cygwin* or darwin* hosts.])],
+    [link Octave and its shared libraries with all dependencies, not just those immediately referenced (should not be needed on most systems).  This is done by default for cygwin* hosts.])],
   [case $enableval in
      yes) link_all_deps=yes ;;
      no)  link_all_deps=no ;;

m4/acinclude.m4

@@ -2109,12 +2109,6 @@ AC_DEFUN([OCTAVE_CHECK_QT_VERSION], [AC_MSG_CHECKING([Qt version $1])
           if test -z "$QT_LIBS"; then
             QT_LDFLAGS="`$PKG_CONFIG --libs-only-other $QT_MODULES | tr ' ' '\n' | $GREP -e '-F' | uniq | tr '\n' ' '`"
             QT_LIBS="`$PKG_CONFIG --libs-only-other $QT_MODULES | tr ' ' '\n' | $GREP -v -e '-F' | uniq | tr '\n' ' '`"
-            ## Enabling link_all_deps works around libtool's imperfect handling
-            ## of the -F flag
-            if test -n "$QT_LDFLAGS"; then
-              link_all_deps=yes
-            fi
-            AM_CONDITIONAL([AMCOND_LINK_ALL_DEPS], [test $link_all_deps = yes])
           fi
         ;;
       esac