glsl: remove execute bit and shebang from python tests

Just like the rest of the tree - these should be run either as part of
the build system check target, or at the very least with an explicitly
versioned python executable.

Fixes: db8cd8e3 ("glcpp/tests: Convert shell scripts to a python script")
Fixes: 97c28cb0 ("glsl/tests: Convert optimization-test.sh to pure python")
Fixes: 3b52d292 ("glsl/tests: reimplement warnings-test in python")
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
(cherry picked from commit 48820ed8)
[Andres Gomez: resolve trivial conflicts]
Signed-off-by: Andres Gomez <agomez@igalia.com>

Conflicts:
	src/compiler/glsl/tests/optimization_test.py