Remove SPO index shifting feature in BsplineSet

[ye-luo]

Proposed changes

1. This feature was never activated nor tested. calls to selectBands always set relative=false.
2. It should not be implemented in the current way even if this feature is needed. Thus remove first_spo and last_spo.
3. Remove unused selectBands variants.

What type(s) of changes does this code introduce?

• Refactoring (no functional changes, no api changes)

Does this introduce a breaking change?

• No

What systems has this change been tested on?

epyc-server

Checklist

• • I have read the pull request guidance and develop docs
• • This PR is up to date with the current state of 'develop'
• • Code added or changed in the PR has been clang-formatted
• • This PR adds tests to cover any new code, or to catch a bug that is being fixed
• • Documentation has been added (if appropriate)

[ye-luo]

Test this please

[prckent]

I agree with the rationale.

Also, this is a feature that would be better handled by outside processing should anyone ever need something similar.