glsl: Drop borrow/carry lowerings in favor of nir
Unconditionally lowering prevents GL drivers from natively implementing these ops. Drivers that need lowering should set lower_uadd_carry or lower_usub_borrow on nir_shader_compiler_options to get the nir lowerings.
Tested with dEQP-GLES31.functional.shaders.builtin_functions.integer.*
Edited by M Henning