After building a project for Oculus then disabling the Oculus plugin in the player settings and building for another android device (on a Samsung phone, not sure if that makes a difference but it might) the app won't launch and the logcat shows errors that Gear VR can't be initialized.

Resetting the editor and rebuilding fixes the issue.

From Peter Kuhn: my guess is the oculus plugin is adding the entry to the android manifest that tells it to launch in VR mode - it’s the same one that controlled the old GearVR launch to vr mode too.
It used to be that every time we made a build, the manifest would get regenerated from scratch - but I think in more recent builds of unity it is cached and reused. so if you enable oculus, then disable it, the manifest entry will still be there. (I just observed this recently in a different context)

This seems to be exactly what is happening.