remove use of meta-virtualization

Remove meta-virtualization from any bblayer.conf.samples.  It was
originally added for the python-pyyaml and python-gevent recipes
but better maintained versions of these recipes are provided by
meta-python.

Before this can be done the python-gevent bbappend in the phosphor
layer must be removed.  The version scope was wildcarded to any version
but the patches don't apply to python-gevent_1.2.2, which becomes the
default from meta-python when meta-virt is removed.  Drop the bbappend.

Change-Id: I6658a163460e3c8e63dc7371ffff803a7b6915b5
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>