Remove .ONESHELL Makefile directive so multi-step targets properly fail

[kevin-bates]

#2886 documents an issue where the lint-server Makefile target does not stop when the flake8 portion of the multi-step target encounters a non-zero exit code. Based on initial investigation, there appears to have been a change in behavior between GNU make 3.81 (which I, and probably others, use on our desktops) and 4.2.1 (which is used in CI, with 4.3 being the latest). In versions < 4, the multi-step targets will stop on non-zero exit status, but with versions < 4, that is not the case.

It turns out that the .ONESHELL directive was causing this issue - which makes sense - because only the last command of the target is the status that is checked. Not sure why 3.x versions work - perhaps they don't properly support .ONESHELL.

At any rate, .ONESHELL was added in #2721 and there's no mention during the review as to why. I have confirmed appropriate behavior without the directive so perhaps the reason for it is no longer present or it was thought to be an improvement - especially since desktop builds were still behaving okay. Since this is a fairly serious issue, we should move forward without .ONESHELL and tackle any related issues of that when they come up.

Resolves #2886

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[akchinSTC]

confirmed that once one shell was removed linting and exiting was running as it should

[kevin-bates]

Thanks @akchinSTC. I'm curious what version of make you use.

[akchinSTC]

Thanks @akchinSTC. I'm curious what version of make you use.