Remove deprecated VIIRSFog compositor in favor of DifferenceCompositor

[djhoese]

I was likely the only one using this and it has been deprecated for many years. I just updated Polar2Grid to not use this.

• Closes #xxxx
• Tests added
• Fully documented
• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

Merging #1561 (eed777b) into master (9f135b1) will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1561      +/-   ##
==========================================
- Coverage   92.18%   92.06%   -0.12%     
==========================================
  Files         251      251              
  Lines       36777    36073     -704     
==========================================
- Hits        33902    33211     -691     
+ Misses       2875     2862      -13     

Flag	Coverage Δ
behaviourtests	4.31% <ø> (-0.19%)	⬇️
unittests	92.61% <ø> (-0.11%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/composites/viirs.py	86.51% <ø> (+2.61%)	⬆️
satpy/tests/features/steps/steps-load.py	49.12% <0.00%> (-6.94%)	⬇️
satpy/tests/reader_tests/test_vii_l2_nc.py	93.93% <0.00%> (-6.07%)	⬇️
...ts/features/steps/steps-real-load-process-write.py	30.76% <0.00%> (-4.95%)	⬇️
satpy/tests/reader_tests/test_vii_l1b_nc.py	97.18% <0.00%> (-2.82%)	⬇️
satpy/readers/maia.py	19.27% <0.00%> (-1.90%)	⬇️
satpy/readers/sar_c_safe.py	50.88% <0.00%> (-1.89%)	⬇️
satpy/tests/reader_tests/test_nwcsaf_msg.py	96.63% <0.00%> (-1.69%)	⬇️
satpy/readers/abi_base.py	93.00% <0.00%> (-1.59%)	⬇️
satpy/readers/goes_imager_nc.py	63.88% <0.00%> (-1.59%)	⬇️
... and 145 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9f135b1...eed777b. Read the comment docs.

[ghost]

DeepCode failed to analyze this pull request

Something went wrong despite trying multiple times, sorry about that.
Please comment this pull request with "Retry DeepCode" to manually retry, or contact us so that a human can look into the issue.