fa3e0da policy: Treat taproot as always active (MarcoFalke)

Pull request description:

  Now that taproot is active, it can be treated as if it was always active for policy for the next major release. This simplifies the code and changes two things:

  * Importing `tr` descriptors can be done before the chain is fully synced. This is fine, because the wallet will already generate `tr` descriptors by default (regardless of the taproot status) after commit 47fe744.
  * Valid taproot spends won't be rejected from the mempool before taproot is active. This is strictly speaking a bugfix after commit 47fe744, since the wallet may generate taproot spends before the chain is fully synced. For example, a slow node or a purposefully offline node. Currently, the wallet needs the mempool to account for change. See bitcoin#11887.

  A similar change was done for segwit v0 in bitcoin#13120 .

  This effectively reverts commit c5ec036.

ACKs for top commit:
  mjdietzx:
    Code Review ACK fa3e0da
  achow101:
    ACK fa3e0da
  sipa:
    utACK fa3e0da
  gruve-p:
    ACK bitcoin@fa3e0da
  gunar:
    Code Review + tACK fa3e0da
  rajarshimaitra:
    code review + tACK bitcoin@fa3e0da

Tree-SHA512: c6dc7a4e6c345bdec33f256847dc63906ab1696aa683ab9b32a79e715613950884ac3a1a7a44e95f31bb28e58dd64679a616175f7e152b21f5550f3337c8e622

40e871d [miner] always assume we can create witness blocks (glozow)

Pull request description:

  Given the low possibility of a reorg reverting the segwit soft fork, there is no longer a need to check whether segwit is active to see if it's okay to add to the block template (see also #23512, #21009, etc). `TestBlockValidity()` is also run on the block template at the end of `CreateNewBlock()`, so any invalid block would be caught there.

ACKs for top commit:
  gruve-p:
    ACK 40e871d
  jnewbery:
    utACK 40e871d, although I disagree about changing the test for segwit transaction in mempool before activagtion, instead of just removing it: #24421 (comment).
  achow101:
    ACK 40e871d
  theStack:
    Code-review ACK 40e871d

Tree-SHA512: bf4860bf2bed8339622d05228d11d60286edb0c32a9a3c434b8d154913c07ea56e50649f4af7009c2a1c6a58a81d2299ab43b41a6f16dee7d08cc89cc1603019