Bugfix for BAM index bins

[valeriuo]

1. Fixes a bug: ArrayIndexOutOfBoundsException would be thrown if levelNumber is too big.
2. Fixes a bug: the level size for the last level was miscalculated. It should be 32768 (2^15).
3. Removes the unused method regionToBins, whose code was already implemented in the class GenomicIndexUtil.

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)

[codecov-io]

Codecov Report

Merging #1024 into master will increase coverage by 0.046%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##              master     #1024       +/-   ##
===============================================
+ Coverage     66.072%   66.118%   +0.046%     
- Complexity      7554      7562        +8     
===============================================
  Files            532       532               
  Lines          32227     32241       +14     
  Branches        5491      5489        -2     
===============================================
+ Hits           21293     21317       +24     
+ Misses          8778      8768       -10     
  Partials        2156      2156

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/htsjdk/samtools/AbstractBAMFileIndex.java	81.882% <100%> (+4.855%)	43 <5> (+4)	⬆️
...a/htsjdk/samtools/cram/encoding/rans/Decoding.java	82.143% <0%> (-3.571%)	11% <0%> (-1%)
src/main/java/htsjdk/samtools/util/IOUtil.java	34.783% <0%> (-0.58%)	71% <0%> (ø)
...rc/main/java/htsjdk/samtools/SamFileValidator.java	85.082% <0%> (-0.025%)	79% <0%> (+2%)
...n/java/htsjdk/samtools/util/SortingCollection.java	70% <0%> (ø)	14% <0%> (ø)	⬇️
...a/htsjdk/samtools/util/AbstractProgressLogger.java	40.385% <0%> (+0.385%)	6% <0%> (ø)	⬇️
...va/htsjdk/samtools/util/AbstractLocusIterator.java	66.292% <0%> (+0.974%)	61% <0%> (+2%)	⬆️
...ain/java/htsjdk/samtools/SAMFileWriterFactory.java	64.138% <0%> (+1.379%)	47% <0%> (ø)	⬇️
...samtools/util/AsyncBlockCompressedInputStream.java	76% <0%> (+4%)	13% <0%> (+1%)	⬆️

[lbergelson]

@droazen Could you take a look at this?

[valeriuo]

Hi! Can I get a review on this PR?

[pshapiro4broad]

Unnecessary getPath() here and below, you can just write new File(BAM_FILE + ".bai"). Although BAM_FILE is otherwise unused here so you could just define BAI_FILE instead.