package.json: remove 'workspaceContains' from activation events

It's not too late to start the work when a Go file is open.
Go became popular so it's not uncommon to see a large repo that
contains some go files.

Also activate it if go.sum or go template files are open.
onLanguage:go.mod and onLanguage:go.work are unnecessary according to
vscode's diagnostics - the existence of language contribution config
makes vscode auto-handle the activation.

Fixes #3038
Fixes #2164

Change-Id: I3ca55316b00cbe7fc82ed01be65cce83d88b9053
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/545136
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Commit-Queue: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Hyang-Ah Hana Kim <hyangah@gmail.com>

package.json

@@ -95,9 +95,8 @@
   },
   "activationEvents": [
     "onLanguage:go",
-    "workspaceContains:*.go",
-    "workspaceContains:*/*.go",
-    "workspaceContains:*/*/*.go",
+    "onLanguage:go.sum",
+    "onLanguage:gotmpl",
     "onDebugInitialConfigurations",
     "onDebugResolve:go",
     "onWebviewPanel:welcomeGo"
@@ -132,8 +131,7 @@
       {
         "id": "go.mod",
         "filenames": [
-          "go.mod",
-          "gopls.mod"
+          "go.mod"
         ],
         "aliases": [
           "Go Module File"