removes summarize_otu_by_cat.py in favor of collapse_samples.py

:beers: for code deletion! 

~~**NOT READY FOR MERGE**~~, I want to fix a small issue I discovered. 

@jairideout or @ElDeveloper, can one of you review this?
Can you add `inplace=True`?  I know this is enabled by default but explicitly passing it will prevent silent bugs in the future if the default changes (since there aren't any unit tests for this functionality).