Remove certificates, they are obsolete and are out of sync (#131)

* Delete GeoTrustGlobalCA_Root.cer

This Cert has been removed from the NINA firmware long time ago arduino/nina-fw@53580a0#diff-88545c89de17b94ff13f555cea95c4971daff07b1e887f1acb0811e7a674347cL545-L572. Furthermore, is about to expire.

* remove old certs not present anymore in the nina-fw

* remove certs already bundled in the nina-fw

* update documentation

* remove workflow that checks for the certificates expire date: there are no more certs in this repo

Author: umbynos

.github/workflows/check-certificates.yml

@@ -83,6 +83,9 @@ previous certificates are going to be erased. To overcome this it's required to
 ./arduino-fwuploader certificates flash --url arduino.cc:443,google.com:443 --file ~/Downloads/my_self_signed_.der -b arduino:mbed_nano:nanorp2040connect -a /dev/ttyACM0
 ```
 
+You can find the certificates that are preflashed on the NINA module
+[here](https://github.com/arduino/nina-fw/blob/master/data/roots.pem).
+
 ### Command line options
 
 The full list of command line options can be obtained with the `-h` option: `./arduino-fwuploader -h`