p2p: Remove BIP61 reject messages

Summary:

Reject messages (BIP 61) appear in the following settings:

• Parsing of reject messages (in case -debug=net is set, off by default). This has only been used for a single LogPrint call for several releases now. Such logging is completely meaningless to us and should thus be removed.
• The sending of reject messages (in case -enablebip61 is set, off by default). This can be used to debug a node that is under our control. Instead of hacking this debugging into the p2p protocol, it could be more easily achieved by parsing the debug log. (Use -printtoconsole to have it as stream, or read from the debug.log file like our python function assert_debug_log in the test framework does)
  
  Having to maintain all of this logic and code to accommodate debugging, which can be achieved by other means a lot easier, is a burden. It makes review on net processing changes a lot harder, since the reject message logic has to be carried around without introducing any errors or DOS vectors.

Backport of Core PR15437

Test Plan: ninja && ninja check-all

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7981