Merge bitcoin/bitcoin#23882: doc: testnet3 was not reset and is doing BIP30 checks again

fa1a51c doc: testnet3 was not reset and is doing BIP30 checks again (MarcoFalke)

Pull request description:

ACKs for top commit:
  theStack:
    ACK fa1a51c

Tree-SHA512: 793eccda583a3edb056b142c36a09a5c867f61d90b96e15e6643417d62eb651eb2f3429c5f245bdb062d18ab9bb05b5048c0888aa5a492cb7bb21a2f3f52324e

Author: fanquake

src/validation.cpp

@@ -2006,9 +2006,8 @@ bool CChainState::ConnectBlock(const CBlock& block, BlockValidationState& state,
     // another edge case to deal with.
 
     // testnet3 has no blocks before the BIP34 height with indicated heights
-    // post BIP34 before approximately height 486,000,000 and presumably will
-    // be reset before it reaches block 1,983,702 and starts doing unnecessary
-    // BIP30 checking again.
+    // post BIP34 before approximately height 486,000,000. After block
+    // 1,983,702 testnet3 starts doing unnecessary BIP30 checking again.
     assert(pindex->pprev);
     CBlockIndex* pindexBIP34height = pindex->pprev->GetAncestor(m_params.GetConsensus().BIP34Height);
     //Only continue to enforce if we're below BIP34 activation height or the block hash at that height doesn't correspond.