mgr: excise CephFS client from mgr C++ base

mgr: excise CephFS client from mgr C++ base

Linking to the client causes two copies of the Client library to be linked in
the ceph-mgr when modules also dynamically link to libcephfs via the "cephfs"
python library. This creates problems with duplicate boost::locale.

Instead, modules should just use the "cephfs" library to send commands to the
MDS.

Signed-off-by: Patrick Donnelly <pdonnell@ibm.com>