DOC: remove inplace usage from docstring examples
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Removes the inplace=True usage examples from the docstring examples. 
Removed 2 additional examples advertising copy=False is using `copy` discouraged as well? I may have missed that

if so, no objections, lgtm copy=False will be the new default with CoW. copy=True can be done through ``df.func().copy()``, so we will propose removing the copy argument as well in PDEP7. Copy won't have any use in the future, so should remove the reference I guess. makes sense, thanks! anything else you wanted to get in here or good to merge? Nothing I can think of right now, so good to go I think let's ship it, thanks @phofl !