Remove RPC calls to get/set UAHF time.

Summary:
Now that the fork occured, there is really no point. Keeping the command line option so I can put the integration tests back in shape using it and then it'll have to go as well.

Depends on D406

Test Plan:

make check

Reviewers: freetrader, #bitcoin_abc, CCulianu

Reviewed By: #bitcoin_abc, CCulianu

Subscribers: CCulianu

Differential Revision: https://reviews.bitcoinabc.org/D407