mesa: Remove GL_ARB_sampler_object depth compare error checking.

mesa: Remove GL_ARB_sampler_object depth compare error checking.

Version 3: Simplify the code comment, word wrap commit description.

Version 2: Return GL_FALSE if ARB_shadow is unsupported instead of
pretending to store the value as suggested by Brian Paul.

This fixes a GL error warning on r200 in Wine.

The GL_ARB_sampler_objects extension does not specify a dependency on
GL_ARB_shadow or GL_ARB_depth_texture for setting the depth texture
compare mode and function. Silently ignore attempts to change these
settings. They won't matter without a depth texture being assigned
anyway.

Reviewed-by: Brian Paul <brianp@vmware.com>