Indirect GLX corner case cleanups

First patch removes some dead dispatch paths for some extensions we don't really support. The second case removes a similar workaround to handle GL_EXT_texture_object "needing" different dispatch than the GL 1.1 texture object functions, but like... what machine are you talking to that only has 1.0 + EXT_texture_object, and if that's what you care about can you please take the rest of indirect GLX too.

My longer term plan here is to split indirect support out at the vnd level, which would allow this all to be restored without special-casing indirect GLX. In the meantime if you need a libGL that can do this use the amber branch.

cc @idr who I'm pretty sure wrote the indirect exception stuff for this and/or has an opinion about interop here.