Clarify Gnarly required annotations

[ldgauthier]

[codecov[bot]]

Codecov Report

Merging #7854 (4956556) into master (752ee3c) will increase coverage by 0.001%. The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #7854       +/-   ##
===============================================
+ Coverage     86.944%   86.946%   +0.001%     
- Complexity     36932     36933        +1     
===============================================
  Files           2219      2219               
  Lines         173666    173666               
  Branches       18754     18754               
===============================================
+ Hits          150993    150995        +2     
+ Misses         16058     16055        -3     
- Partials        6615      6616        +1     

Impacted Files	Coverage Δ
...tools/walkers/gnarlyGenotyper/GnarlyGenotyper.java	83.168% <ø> (ø)
...itute/hellbender/tools/LocalAssemblerUnitTest.java	92.448% <0.000%> (ø)
.../hellbender/utils/python/PythonUnitTestRunner.java	78.689% <0.000%> (+3.279%)	:arrow_up:

[ldgauthier]

Taking out mention of the deprecated MQ_DP annotation, corresponds with https://docs.google.com/document/d/1ZdRERavtO1k4v0ppVzJ7gu6PHzSydznhYDmvZUb8qPo/edit?usp=sharing