Reconsider removing inst()

[AshesITR]

The search from the original issue #1643 shows four packages using devtools::inst() as of now:

• NlsyLinks, last updated 4 years ago
• Wats, last updated 5 years ago
• teachingApps, last updated 2 years ago; no longer using devtools::inst()
• IalsaSynthesis, last updated 5 years ago

Since the three remaining packages with an actual dependency only have the dependency in their tests and none of them seem to be actively maintained, I would suggest to remove devtools::inst() from the package once again.

The upside of this would be that the auto-complete prefix for devtools::install() shortens to "i" instead of "insta", saving a lot of keystrokes for this very frequent function call.
Also, it's less confusing than to have two functions with very similar name but completely different functionality.