Remove the "OP_" prefix from transaction script decodes.

This set of changes was born out of the discussion of #5264.

The main impact of these changes is on the scriptPubKey "asm" value in the output for transaction decodes. There are also more minor logging and bitcoin-tx references.

Basically, the goal was to just remove the "OP_" prefixes.

1) Example P2PKH
Before:
OP_DUP OP_HASH160 b9c670c7aa955c9808af7eeb9643b9fd6285cbf5 OP_EQUALVERIFY OP_CHECKSIG
After:
DUP HASH160 b9c670c7aa955c9808af7eeb9643b9fd6285cbf5 EQUALVERIFY CHECKSIG

2) Example P2SH
Before:
OP_HASH160 2a5edea39971049a540474c6a99edf0aa4074c58 OP_EQUAL
After:
HASH160 2a5edea39971049a540474c6a99edf0aa4074c58 EQUAL

If these changes gain acceptance, I'll add some release notes too when that time comes.