Be more explicit about the removal of rebin

[mwcraig]

Not sure this really warrants a pull request, but....fixes #779

[codecov]

Codecov Report

Merging #780 (577ddcd) into main (9619eaf) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #780   +/-   ##
=======================================
  Coverage   97.29%   97.29%           
=======================================
  Files           9        9           
  Lines        1403     1403           
=======================================
  Hits         1365     1365           
  Misses         38       38           

Impacted Files	Coverage Δ
ccdproc/core.py	97.54% <100.00%> (ø)

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