test: Remove useless test_bitcoin_main.cpp

Summary:
Partial backport of core PR15504:
https://github.com/bitcoin/bitcoin/pull/15504/commits/fa02b222459d46219c23366218c5b4e9ba768aeb

Test Plan:

ninja check
make check # autotools build

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D5481