security/pinentry-gnome3: De-version and rename

Due to the new GNOME versioning scheme, security/pinentry-gnome3 has
been renamed to security/pinentry-gnome and all references to
"GNOME 3" have been dropped in favor of just "GNOME". The binary itself
still installs as pinentry-gnome3 at this time, however.

Rename the option GNOME3 -> GNOME in security/pinentry.

PR: 263681
Reported by: PauAmma <pauamma@gundo.com>