mesa: Drop bitfield "enums" from the enum-to-string table.

mesa: Drop bitfield "enums" from the enum-to-string table.

Asking the table for bitfield names doesn't make any sense.  For 0x10, do
you want GL_GLYPH_HORIZONTAL_BEARING_ADVANCE_BIT_NV or
GL_COLOR_BUFFER_BIT4_QCOM or GL_POLYGON_STIPPLE_BIT or
GL_SHADER_GLOBAL_ACCESS_BARRIER_BIT_NV?  Giving a useful answer would
depend on a whole lot of context.

This also fixes a bad enum table entry, where we chose GL_HINT_BIT instead
of GL_ABGR_EXT for 0x8000, so we can now fix its entry in the enum_strings
test.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>