mesa: remove stale comment

This line stopped making sense in the great sed
replace of commit f9995b30756140724f41daf963fa06167912be7f
mesa: remove outdated comment

No such argument exists since this commit:

commit 92f3fca0ea429dcf07123e63447449db53308266
Author:     Ian Romanick <ian.d.romanick@intel.com>
AuthorDate: Sun Aug 21 17:23:58 2011 -0700
Commit:     Ian Romanick <ian.d.romanick@intel.com>
CommitDate: Tue Aug 23 14:52:09 2011 -0700

    mesa: Remove target parameter from dd_function_table::BufferSubData
mesa: use STATIC_ASSERT()
mesa: remove handcounted magic number
mesa: extend get_texobj for multitexturing
mesa: add helper functions for TexParameter* funcs
mesa: clarify error message
mesa: improve debug message
main: add _mesa_get_and_init_texture()

Needed for GL_EXT_direct_state_access.
mesa: pull out texture object lookup in TexImage*D code

Prepare for GL_EXT_direct_state_access entrypoints.
mesa: add _mesa_get_tex_unit()
mesa: pull out texture object lookup in TexImage*D code

Prepare for GL_EXT_direct_state_access entrypoints.
mesa: lift texture lookup out of error checking

Have callers do it instead.
mesa: reconsolidate teximage checking
mesa: lift texture lookup out of error checking

Only lookup the texture object once.
mesa: lift texture lookup out of error checking again

Only lookup the texture object once.
mesa: lift texture lookup out of error checking again again

Split out the large switch statement to its own function.

And only lookup the texture object once.
mesa: lift texture lookup to caller for Tex*Multisample functions
mesa: factor out _mesa_max_tex_unit()

This is about to appear in a lot more places, so
reduce boilerplate copy paste.
mesa: add glMultiTexSubImage*DEXT() functions