[LINTER] Remove empty lines at the beginning of a block

Summary:
Follow-up for https://reviews.bitcoinabc.org/D4678?id=14718#inline-29056

Documentation:
https://releases.llvm.org/8.0.0/tools/clang/docs/ClangFormatStyleOptions.html

Test Plan:
Return no error:

arc lint --everything

Edit src/init.cpp and add an empty newline after any opening block.

arc lint -- src/init.cpp

Check the linter proposes to remove the newline.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D4754