Remove auto_nbands handling + fix bravais inconsistency handling

[esoteric-ephemera]

Major changes:

• Change auto_nbands to only throw a warning and not attempt to change the VASP job, as per original intention. VASP already updates NBANDS to accommodate parallelization settings so the handler here is doing more harm (esp. in bandstructure sweeps) than good
• Update the bravais handling to reflect advice from VASP devs and the docstr that's there

[codecov-commenter]

Codecov Report

❌ Patch coverage is 12.00000% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.17%. Comparing base (32858c3) to head (2556a3e).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/custodian/vasp/handlers.py	0.00%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #409      +/-   ##
==========================================
+ Coverage   53.02%   53.17%   +0.14%     
==========================================
  Files          39       39              
  Lines        3508     3500       -8     
==========================================
+ Hits         1860     1861       +1     
+ Misses       1648     1639       -9     

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