mesa: OpenGL 1.3 feature GL_ARB_texture_cube_map is not optional

mesa: OpenGL 1.3 feature GL_ARB_texture_cube_map is not optional

Cheatsheet:

_mesa_has_ARB_texture_cube_map() becomes (true &&
ctx->Extensions.Version >=
_mesa_extension_table[...].version[ctx->API]).  The last value is 0 when
ctx->API is API_OPENGL_COMPAT and ~0 otherwise.  The whole function
effectively becomes (ctx->API == API_OPENGL_COMPAT).

_mesa_has_OES_texture_cube_map() becomes (true &&
ctx->Extensions.Version >=
_mesa_extension_table[...].version[ctx->API]).  The last value is 0 when
ctx->API is API_OPENGLES and ~0 otherwise.  The whole function
effectively becomes (ctx->API == API_OPENGLES).

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14203>