remove warmup wait dead code to prevent accidental deadlock

Since we should never have a front-end thread wait for background
thread, having a warmup wait logic will ensure that we do not use
it accidentally in the future and cause a deadlock

Change-Id: I28ec96dceaffa02810415402226df20f8eb44cc7
Reviewed-on: http://review.couchbase.org/41206
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Sundararaman Sridharan <sundar@couchbase.com>