Defuse a ticking time-bomb by removing the dependency on devel/bzr.

It is likely that this will break "make test", so, why am I doing it?

The answer is that devel/bzr unconditionally depends on python27 (it is
known not to build with python37) -- and python27 is imminently due for
removal (see PR 249337).

This would not matter so much except that py-pip winds up a dependency
of devel/cmake, and thus, over 2000 ports -- all of which would have
broken when python27 was removed.

Unfortunately the time before that removal happens is simply too short
to have a proper discussion with all stakeholders.  We need to remove
the dependency immediately so that PR 249337 can proceed.

PR:		249337 (related to)

devel/py-pip/Makefile

@@ -37,7 +37,6 @@ TEST_DEPENDS=	${PYTHON_PKGNAMEPREFIX}cryptography>=0:security/py-cryptography@${
 		${PYTHON_PKGNAMEPREFIX}virtualenv>=0:devel/py-virtualenv@${PY_FLAVOR} \
 		${PYTHON_PKGNAMEPREFIX}werkzeug>=0:www/py-werkzeug@${PY_FLAVOR} \
 		${PYTHON_PKGNAMEPREFIX}wheel>=0:devel/py-wheel@${PY_FLAVOR} \
-		bzr:devel/bzr \
 		hg:devel/mercurial \
 		git:devel/git \
 		svn:devel/subversion