internal/lsp: only show command errors once
internal/lsp: only show command errors once

We both showing errors as a popup and returning them to the client,
which would then most likely show them as a popup. Don't return errors
back to the client.

Change-Id: I8486534e19399d514752900025d6db8db85d5086
Reviewed-on: https://go-review.googlesource.com/c/tools/+/272090
Trust: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
Run-TryBot: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
gopls-CI: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools