mesa: don't enable glVertexPointer() when using API_OPENGLES2.

mesa: don't enable glVertexPointer() when using API_OPENGLES2.

This function is only present in GLES1 and in the OpenGL compatibility
profile.

Fixes the following "make check" failure:

    [----------] 1 test from DispatchSanity_test
    [ RUN      ] DispatchSanity_test.GLES2
    Mesa warning: couldn't open libtxc_dxtn.so, software DXTn
    compression/decompression unavailable
    dispatch_sanity.cpp:122: Failure
    Value of: table[i]
       Actual: 0x4de54e
    Expected: (_glapi_proc) _mesa_generic_nop
    Which is: 0x41af72
    i = 321
    [  FAILED  ] DispatchSanity_test.GLES2 (4 ms)
    [----------] 1 test from DispatchSanity_test (4 ms total)

NOTE: This is a candidate for stable release branches.

Reviewed-by: Oliver McFadden <oliver.mcfadden@linux.intel.com>
Tested-by: Oliver McFadden <oliver.mcfadden@linux.intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>