Revert "[SP] Also install jagame/jk2game shared object to the base folder"

This reverts commit 6f8801fd635d33c7a753f23014b259daaa29e604.
[SP] Don't fallback to looking in base for jagame/jk2game.  Fallback to OpenJK.
[MP] Some game dll load function cleanup.
[SP] Fix cg_main.h header guard define.
[SP] Just remove cg_main.h entirely.
Merge branch 'master' of https://github.com/JACoders/OpenJK