Remove full-screen support from GHOST API's.
Note that this only had back-end implements for X11 and WIN32.
This was last used for the Game Engine to run games full-screen,
removing as it's unused and it doesn't seem likely to be used in the
future.
This doesn't impact making Blender full-screen from the window menu
which uses a window decoration setting.
Ref: !137050
f459d97dfd