Trivial: Fix validation comments

- Move comment about transaction/block weight calculation so it applies not only to the GetBlockWeight function but also to GetTransactionWeight
- Fix comment in validation.cpp referencing future deployment of BIP113. It has already been deployed.
- The doc comment for BLOCK_DOWNLOAD_WINDOW wasn't updated since pruning was introduced, so it still refers to pruning as something that might happen in the future. A larger BLOCK_DOWNLOAD_WINDOW window would now, indeed, make pruning harder.

src/validation.h

@@ -94,8 +94,8 @@ static const int MAX_CMPCTBLOCK_DEPTH = 5;
 static const int MAX_BLOCKTXN_DEPTH = 10;
 /** Size of the "block download window": how far ahead of our current height do we fetch?
  *  Larger windows tolerate larger download speed differences between peer, but increase the potential
- *  degree of disordering of blocks on disk (which make reindexing and in the future perhaps pruning
- *  harder). We'll probably want to make this a per-peer adaptive value at some point. */
+ *  degree of disordering of blocks on disk (which make reindexing and pruning harder). We'll probably
+ *  want to make this a per-peer adaptive value at some point. */
 static const unsigned int BLOCK_DOWNLOAD_WINDOW = 1024;
 /** Time to wait (in seconds) between writing blocks/block index to disk. */
 static const unsigned int DATABASE_WRITE_INTERVAL = 60 * 60;