[rpc] Deprecate estimatefee RPC

Summary:
Deprecate estimatefee in v0.16, for final removal in v0.17.

This commit introduces a phased removal of RPC methods. RPC method is
disabled by default in version x, but can be enabled by using the
-deprecatedrpc=<method> argument. RPC method is removed entirely in
version (x+1).

[rpc] [tests] Add deprecated RPC test

This is a backport of Core PR11031

Test Plan:

make check
./test/functional/test_runner.py --extended

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1920