remove Makefile-pl on make distclean
TS-2195: reimplement TSHttpTxnCacheLookupSkip in terms of TSHttpTxnConfigIntSet

Replace the guts of TSHttpTxnCacheLookupSkip with TSHttpTxnConfigIntSet.
This is a compatible change that makes it easy to remove
TSHttpTxnCacheLookupSkip in the 5.x branch.
initialize HttpTunnelProducer::last_state to a default value