Revert "CA-100400: GC event queue based on size rather than number."

This reverts commit 2f32598b8544317d332796a4b44a2a99f212edf3.
Revert "CA-100400: Store the event size alongside the event in the event.next queue"

This reverts commit c8e51d598760c5f79f0ab7f20b79f0c0c21b1e87.
Revert "Import xapi_event.ml from trunk"

This reverts commit 5a42c61e6f229cdf0b782b57f12595b3b7ed0d4a.
Revert "quicktest: add a test case for parallel calls to event.from"

This reverts commit b36e85ee1802f0fb11bb37681a36aa08055510f7.
Merge remote-tracking branch 'creedence/master' into xs64bit-ring3

Reverted xapi event changes for CA-100400 on creedence.