Disable copying of CWalletTx objects to prevent bugs where instances get copied
in and out of the mapWallet map and fields are updated in the wrong copy.
This is a backport of Core PR9381 [4/5]
https://github.com/bitcoin/bitcoin/pull/9381/commits/d002f9d15d938e78360ad906f2d74a249c7e923e
Depends on D9076