Return instead of panic in code that is only used in dev

[catsby]

This bit of code causes an issue in at least AWS ECS server installs using on-demand runners, where a release will fail:

! Unrecognized remote plugin message:
  This usually means that the plugin is either invalid or simply
  needs to be recompiled to support the latest protocol.

The underlying issue is a panic during the init phase caused by something that's only used in development, so here we change that to simply return.

UPDATE: refactored/rebased to completely exclude internal/assets/dev.go from builds with the assetsembedded tag (see the Makefile for reference). The dev.go file was generating dev_assets.go which was not included in builds, however the dev.go file itself still was, and it's init() method could cause troubles

[krantzinator]

Even if for development purposes, should we still return a more friendly error message? For our future selves 😅

[catsby]

Even if for development purposes, should we still return a more friendly error message? For our future selves 😅

@krantzinator Normally I would say yes, however in this situation we don't have any logging or error returns at all

[mitchellh]

This is ancient. I'd be curious if we even need this at all anymore (the dev stuff). This was basically for us to build Waypoint with go build before we had the CEB done. Since we always make install or equivalent now I wonder if we can just throw it away.