x/tools/gopls: improve output for subcommands with no flags

[ainar-g]

Currently (golang/tools@6375436), the output of gopls check -h looks like this:

show diagnostic results for the specified file

Usage: check [flags] <filename>

Example: show the diagnostic results of this file:

  $ gopls check internal/lsp/cmd/check.go

	gopls check flags are:

That is, no flags are documented. If gopls check actually has flags, they should probably be documented, and if not, the output should probably not mention them at all.

[rentziass]

I believe this was fixed by golang.org/cl/284215?

[ainar-g]

@rentziass, I've checked gopls from master, and the message is better, but there is still the [flags] in there:

$ gopls check -h
  show diagnostic results for the specified file

  Usage: check [flags] <filename>

  Example: show the diagnostic results of this file:

    $ gopls check internal/lsp/cmd/check.go

Ironically, the -h flag, which I used to get this message, isn't documented in the message itself.

[rentziass]

I see, that probably doesn't come from the commands themselves but something higher up. Let me have a look.

[gopherbot]

Change https://golang.org/cl/357994 mentions this issue: internal/tool: remove [flags] when not necessary