build/ops: rpm: stop install-deps.sh clobbering spec file Python build setting

build/ops: rpm: stop install-deps.sh clobbering spec file Python build setting

Fedora 29 still ships a Python 2 binary, but some of Ceph's build
dependencies are only available in py3 versions there. In other
words, from F29 on, it is no longer possible to do a py2 Ceph build
on Fedora, even if a python2 binary exists on the system.

If that were not enough, the Python 2 that ships with Fedora 29 is
linked against a non-compatible version of OpenSSL.

Before this commit, install-deps.sh was overriding the spec file's
Python build setting based on the presence or absence of a python2
binary. As the bug cited below indicates, this was not a good idea.

It's better for the spec file to be explicit about which OS versions
are py2 and which are py3, and just stick to that.

Fixes: http://tracker.ceph.com/issues/37301
Signed-off-by: Brad Hubbard <bhubbard@redhat.com>
Signed-off-by: Nathan Cutler <ncutler@suse.com>