[backport#12542] Remove redundant includes. Conform to header include guidelines.
Summary:
7ef46d063a Remove redundant includes. Conform to header include guidelines. (practicalswift)
Pull request description:
From the header include guidelines ([developer-notes.md](https://github.com/bitcoin/bitcoin/blob/master/doc/developer-notes.md#source-code-organization)): > "One exception is that a `.cpp` file does not need to re-include the includes already included in its corresponding `.h` file." Covered in this PR: * `rpc/util.h` includes `pubkey.h` + `utilstrencodings.h`. `rpc/util.cpp` includes `rpc/util.h`. * `util.h` includes `fs.h`. `util.cpp` includes `util.h`.
Backport of Core PR12542
Test Plan:
ninja all check check-functional
Reviewers: #bitcoin_abc, PiRK
Reviewed By: PiRK
Differential Revision: https://reviews.bitcoinabc.org/D8210