mesa: Remove EXT_bgra and EXT_texture_format_BGRA8888 extension enable flags

mesa: Remove EXT_bgra and EXT_texture_format_BGRA8888 extension enable flags

All drivers remaining in Mesa support this extension.  This extension
is either required or optional features in desktop OpenGL, OpenGL ES
1.x, and OpenGL ES 2.x.

EXT_texture_format_BGRA8888 is mostly a subset of EXT_bgra.  The only
difference seems to be that EXT_texture_format_BGRA8888 allows GL_BGRA
as an internal format to glTexImage2D and friends.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>