[mempool] MemPoolRemovalReason for CTxMemPool::removeWithAnchor

[ch4ot1c]

See:
https://github.com/zcash/zcash/blob/333b9a0d0b0db2ada9f106ac73cef22a77914ec7/src/txmempool.cpp#L209
https://github.com/zcash/zcash/blob/333b9a0d0b0db2ada9f106ac73cef22a77914ec7/src/txmempool.cpp#L125

CTxMemPool::remove has been replaced by removeRecursive. Additionally, the MemPoolRemovalReason from Bitcoin does not include a case to handle CTxMemPool::removeWithAnchor:

If a block is disconnected from the tip, and the root changed,
we must invalidate transactions from the mempool which spend
from that root -- almost as though they were spending coinbases
which are no longer valid to spend due to coinbase maturity.

Perhaps this calls for a REANCHORED MempoolRemovalReason, since it is a slightly different case than the existing CONFLICT option ("Removed for conflict with in-block transaction").

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