test: Set peertimeout in write_config

This avoids having to remember to set it whenever mocktime is used with
peer connections. Also, it might help avoiding disconnects when
attaching a debugger to a running test.

test/functional/feature_csv_activation.py

@@ -94,7 +94,6 @@ class BIP68_112_113Test(BitcoinTestFramework):
         self.num_nodes = 1
         self.setup_clean_chain = True
         self.extra_args = [[
-            '-peertimeout=999999',  # bump because mocktime might cause a disconnect otherwise
             '-whitelist=noban@127.0.0.1',
             '-par=1',  # Use only one script thread to get the exact reject reason for testing
         ]]