Update man page and deprecation warning for binstubs --all

[rreinhardt9]

Resolves #3251

Update the deprecation warning to point the user to the --all option
for bundle binstubs as the preferred way to install binstubs for all
gems in a bundle.

Update bundle binstubs man page to include the --all option 🎉
and remove the note pointing to the now deprecated method of installing
all binstubs.

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[rreinhardt9]

I'm super new to contributing period and to rubygems specifically, so do let me know if there is something I can do to be more helpful because I probably just don't realize it 😆

One question that popped up when working on this; when running bin/rake man:build it creates a bunch of diffs in other places besides just the man page I changed. I get diffs on these output files:

But the weird part is that it's just adding/removing whitespace to balance out the words in the row 🤔

I didn't commit those updates because it seemed like that was probably something with my configuration because otherwise the CI check would have not passed for other branches I would figure. Is that a correct assumption or is should I look more into that?

[deivid-rodriguez]

Thanks so much @rreinhardt9!!