Remove bogus runtime dependency, actually a build time dep

Desipite the protestations of namcap this is bogus. The import setuptools_scm only occurs inside of a try: statement, and on top of that only in an arm that is never even reached. The installed module should always have the generated version file anyway, so python-setuptools-scm should only ever be a makedepends, never a depends. It is possible for python-setuptools to be needed at runtime, but not for the scm variant to be needed unless the build is not being done correctly.