glsl: remove execute bit and shebang from python tests

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: db8cd8e3677 ("glcpp/tests: Convert shell scripts to a python script")
Fixes: 97c28cb0823 ("glsl/tests: Convert optimization-test.sh to pure python")
Fixes: 3b52d292273 ("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>