Remove -mempoolreplacement to prevent needless block prop slowness.

At this point there is no reasonable excuse to disable opt-in RBF,
and, unlike when this option was added, there are now significant
issues created when disabling it (in the form of compact block
reconstruction failures). Further, it breaks a lot of modern wallet
behavior.

doc/man/bitcoin-qt.1

@@ -488,9 +488,6 @@ Relay and mine data carrier transactions (default: 1)
 Maximum size of data in data carrier transactions we relay and mine
 (default: 83)
 .HP
-\fB\-mempoolreplacement\fR
-.IP
-Enable transaction replacement in the memory pool (default: 1)
 .HP
 \fB\-minrelaytxfee=\fR<amt>
 .IP

doc/man/bitcoind.1

@@ -488,10 +488,6 @@ Relay and mine data carrier transactions (default: 1)
 Maximum size of data in data carrier transactions we relay and mine
 (default: 83)
 .HP
-\fB\-mempoolreplacement\fR
-.IP
-Enable transaction replacement in the memory pool (default: 1)
-.HP
 \fB\-minrelaytxfee=\fR<amt>
 .IP
 Fees (in BTC/kB) smaller than this are considered zero fee for relaying,