Remove indexingBin from SAMRecord and only compute it when writing BA…

[tfenne]

…M and during index creation.

Description

Please explain the changes you made here. Explain the motivation for making this change. What existing problem does the pull request solve?

Checklist

• [ ] Code compiles correctly
• [ ] New tests covering changes and new functionality
• [ ] All tests passing
• [ ] Extended the README / documentation, if necessary
• [ ] Is not backward compatible (breaks binary or source compatibility)

[tfenne]

Closing as I cannot get this to work with the long cigar code.