devel/git-cinnabar: simplify MAKE_ENV and MAKE_ARGS

• PYTHON_PATH is no longer used by git-cinnabar itself
• Convert != to ${:!...!}
• Convert /.. to :H

Note, foreign variables can be factored out (dubious benefit):

1. Import devel/git variables (append if :group is missing) .for v in MAKE_ENV MAKE_ARGS WRKSRC:git ${v:S/:/_/}+= ${:!${SETENV} -u FLAVOR ${MAKE} -V ${v:C/:.*//} -C ${PORTSDIR}/devel/git!} .endfor