DOC: remove inplace usage from docstring examples

[phofl]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

Removes the inplace=True usage examples from the docstring examples.

[MarcoGorelli]

Looks good to me pending green

[phofl]

Removed 2 additional examples advertising copy=False

[MarcoGorelli]

is using copy discouraged as well? I may have missed that

if so, no objections, lgtm

[phofl]

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.

[MarcoGorelli]

makes sense, thanks! anything else you wanted to get in here or good to merge?

[phofl]

Nothing I can think of right now, so good to go I think

[MarcoGorelli]

let's ship it, thanks @phofl !