Originally, git was something new, not installed everywhere and had commandline
stability problems. This has changed and git it no longer makes sense to
continually build this when the system installed version is likely sufficient.
This speeds up build since recipes no longer have to wait for git-native to build
if they're fetched from a git:// SRC_URI.
Also add git to the sanity checks and drop the no unneeded svn reference.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
