configure: remove deprecated --{enable, disable}-git-update

The options were deprecated in 6.0.  That said, we do not really have a
formal deprecation cycle for build-time changes, since they do not affect
users.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20211007130829.632254-16-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -1483,14 +1483,6 @@ for opt do
   ;;
   --with-git=*) git="$optarg"
   ;;
-  --enable-git-update)
-      git_submodules_action="update"
-      echo "--enable-git-update deprecated, use --with-git-submodules=update"
-  ;;
-  --disable-git-update)
-      git_submodules_action="validate"
-      echo "--disable-git-update deprecated, use --with-git-submodules=validate"
-  ;;
   --with-git-submodules=*)
       git_submodules_action="$optarg"
   ;;