[sbtc] Remove unused constants in sBTC token contract

[friedger]

Description

Remove unused constants in sBTC token contract

Changes

Removes two constants from contract that were not used.
Removes check-checker and related comments to reduce size of contract

Testing Information

Unit test adapted.
More unit tests added.

Checklist:

• I have performed a self-review of my code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[setzeus]

PR consists of removing unused constant, unused comments & minimal formatting changes (such as error codes in 'sbtc-token').

Only one question re: failed costs at 400 but looks good to me otherwise (assuming 'git is dirty' issue is fixed cc @djordon)

[djordon]

@friedger have you tried running make build locally and pushing the changes up? Sometimes that work, but sometimes not.

[friedger]

I don't know why the check fails due to dirty git. Where get files changed?

[djordon]

We run make build in CI, which generates some files. Here there are some documentation files that get generated based on the clarity source, so if the source changes the documentation will automatically get updated.