glsl: TCS outputs can not be transform feedback candidates on GLES

Avoids regression on:

KHR-GLES*.core.tessellation_shader.single.xfb_captures_data_from_correct_stage

that is uncovered by the following patch.

"glsl: fix recording of variables for XFB in TCS shaders"

v2: Rebased over glsl: fix recording of variables for XFB in TCS shaders
v3: Move this patch before "glsl: fix recording of variables for XFB in TCS
    shaders" to avoid temporal regressions. (Illia Mirkin)

Cc: 19.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
(cherry picked from commit bf1f4948)