builtin: unmark git-switch and git-restore as experimental

builtin: unmark git-switch and git-restore as experimental

In 4e43b7ff (Declare both git-switch and git-restore experimental,
2019-04-25), the newly introduced git-switch(1) and git-restore(1)
commands were marked as experimental. This was done to provide time to
make breaking changes to the interface. It has now been over six years
since these commands were implemented and there hasn't been much change.
Consequently, users have grown to rely on how these commands work and it
is no longer feasible to make any breaking changes.

Let's remove the experimental label for git-switch(1) and
git-restore(1).

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>