CA-137766: Remove GC stats reporting

This code erroneously reported rrdd's GC stats as xapi's. The code has
now been moved to xapi itself, which reports these and other stats to
rrdd via the plugin mechanism.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #23 from johnelse/ca-137766

CA-137766: Remove GC stats reporting