Remove enable_mocktime in rpc_listtransactions
Remove enable_mocktime in rpc_listtransactions

Summary:
Mocktime is unused in the test.
Depends on D2628

Test Plan:
  ./test/functional/test_runner.py rpc_listtransactions

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2629

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