Tramp should only change M-x shell startup when used in tramp buffers

[積丹尼 Dan Jacobson]

I notice in emacs when tramp is running and we do M-x shell, we see the prompt

Remote shell path: /adb::/sdcard/GTs/gpx//system/bin/sh

That is great, but what if we just want an old fashioned local shell
like we see with plain emacs?

I propose if the user does M-x shell when the current directory of the
buffer he is in is just a local directory, then tramp should be
"hands off", and let him proceed the old fashioned way, with no such
scary prompts.

Currently for some reason when tramp starts it causes starting M-x shell
universally to behave different, no matter what buffer it is started
from.

tramp-version "2.4.2"