_content/ref: remove go get from build commands

Fixes golang/go#60110

Change-Id: I4513db35a100695801a29c33783061f1b485197d
Reviewed-on: https://go-review.googlesource.com/c/website/+/494235
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

_content/ref/mod.md

@@ -1425,7 +1425,6 @@ includes:
 * `go build`
 * `go fix`
 * `go generate`
-* `go get`
 * `go install`
 * `go list`
 * `go run`