This removes all explicit mention of SCRIPT_DISALLOW_SEGWIT_RECOVERY from validation.cpp
Changes the current behavior by making it impossible to accept segwit recovery transactions
into the mempool, even if "fRequireStandard" is false (this is the same as with all other
script verify flags that are included in standard flags).
Functional test is amended to replect this change in behavior.
Depends on D3065