Share cache RemovalListener

The removal listener can be easily be shared among instances -- so
create only one shared instance for all ConnectionAdapterImpls.

Change-Id: I3d47d30eb537b86a35f42a69ff590b623a99e035
Signed-off-by: Robert Varga <rovarga@cisco.com>
Signed-off-by: Michal Polkorab <michal.polkorab@pantheon.sk>