Signed-off-by: Mathieu Velten <mathieuv@matrix.org>

* Two scripts are basically entry_points already
* Move and rename scripts/* to synapse/_scripts/*.py
* Delete sync_room_to_group.pl
* Expose entry points in setup.py
* Update linter script and config
* Fixup scripts & docs mentioning scripts that moved

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

this makes docker builds a bit faster.