Remove unused minimal layout

Summary: This layout and it's associated parts are not used anywhere.

Test Plan:
make serve and make sure nothing is broken.
grep -rnI minimal . should contain no references to layouts or styles.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7401