Remove code to disable compile bypass on OSX variants.

There was code added to buildscripts/generate_compile_bypass_expansions.py to disable the compile bypass feature for OSX variants because of a failure to load the .evergreen.yml config file. Once BUILD-4317 gets resolved we should remove this code.

The code added was to function should_bypass_compile()

    # Disable compile bypass for OSX variants.

    # TODO: Remove once BUILD-4317 is resolved.

    if sys.platform == 'darwin':

        return False

...