Include Objective-C source files
Summary:
The copyright_header.py script will process Objective-C source files
(*.mm) as other ones.
Drop no-longer-relevant copyright holder name
This is a backport of core#16314
Depends on D9811
Test Plan: ./contrib/devtools/copyright_header.py report .
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D9812