Removing cruft leftover from JAXB

[lbergelson]

There were some things that could be cleaned up after removing JAXB support for SAMSequenceRecord.

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 #1207 into master will increase coverage by 0.018%.
The diff coverage is 66.667%.

@@              Coverage Diff               @@
##              master    #1207       +/-   ##
==============================================
+ Coverage     68.702%   68.72%   +0.018%     
  Complexity      8061     8061               
==============================================
  Files            542      542               
  Lines          32711    32701       -10     
  Branches        5533     5532        -1     
==============================================
- Hits           22473    22472        -1     
+ Misses          8038     8029        -9     
  Partials        2200     2200

Impacted Files	Coverage Δ	Complexity Δ
...in/java/htsjdk/samtools/SAMSequenceDictionary.java	72.727% <ø> (ø)	45 <0> (ø)	⬇️
...c/main/java/htsjdk/samtools/SAMSequenceRecord.java	79.167% <66.667%> (+8.435%)	34 <0> (ø)	⬇️
...samtools/util/AsyncBlockCompressedInputStream.java	72% <0%> (-4%)	12% <0%> (-1%)
...sjdk/samtools/util/Md5CalculatingOutputStream.java	74.359% <0%> (+7.692%)	8% <0%> (+1%)	⬆️

[jamesemery]

Looks good to me, all low impact removal 👍