Remove unused fAllowFree variable from coincontrolwallet.cpp
Remove unused fAllowFree variable from coincontrolwallet.cpp

Summary: Remove leftovers from D1360.

Test Plan:
  make check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1387

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