Remove some of the reserves and regtest features

[rajarshimaitra]

Description

Currently the way ExternalReserves functionality is written, it can only be used with electrum feature. The tests should fail if the implementation behavior is enforced.. Disabling the tests in CI.

Also removing the regtest-esplora features from the tests, because they won't work when #92 lands.

Notes to the reviewers

Checklists

All Submissions:

• [x] I've signed all my commits
• [x] I followed the contribution guidelines
• [x] I ran cargo fmt and cargo clippy before committing

[rajarshimaitra]

@notmandatory we need to get this one merged before we can make the CI pass for #99 and #102 ..