third_party: Delete mysql.patch.
third_party: Delete mysql.patch.

It was used for compiling Google MySQL but this support was dropped in
https://github.com/vitessio/vitess/pull/420. Therefore, the file is
unreferenced since then.

Signed-off-by: Michael Berlin <d0bd1c6a4289581537082d4e674f75efbec53916@google.com>

alainjobart/vitess,alainjobart/vitess,dcadevil/vitess,HubSpot/vitess,enisoc/vitess,enisoc/vitess,mahak/vitess,davygeek/vitess,mahak/vitess,alainjobart/vitess,alainjobart/vitess,dcadevil/vitess,davygeek/vitess,mahak/vitess,tinyspeck/vitess,davygeek/vitess,alainjobart/vitess,enisoc/vitess,alainjobart/vitess,vitessio/vitess,dcadevil/vitess,tinyspeck/vitess,enisoc/vitess,dcadevil/vitess,tinyspeck/vitess,HubSpot/vitess,vitessio/vitess,alainjobart/vitess,davygeek/vitess,davygeek/vitess,mahak/vitess,HubSpot/vitess,mahak/vitess,HubSpot/vitess,vitessio/vitess,HubSpot/vitess,HubSpot/vitess,vitessio/vitess,davygeek/vitess,tinyspeck/vitess,tinyspeck/vitess,tinyspeck/vitess,dcadevil/vitess,enisoc/vitess,alainjobart/vitess,vitessio/vitess,enisoc/vitess,vitessio/vitess,davygeek/vitess,tinyspeck/vitess,HubSpot/vitess,vitessio/vitess,mahak/vitess,vitessio/vitess,enisoc/vitess,mahak/vitess,dcadevil/vitess,mahak/vitess,dcadevil/vitess,HubSpot/vitess