[release] package.json: do not claim .tmpl files in stable version

https://go-review.googlesource.com/c/vscode-go/+/281392 is a prep work
for template support. However, the handling is not available in gopls
yet, and LSP registration is activated only in the preview mode (per

This CL is the remaining task from cl/283639 to disable the experimental
feature from the stable release. We will revert this change when gopls
is ready to handle templates.

Update golang/vscode-go#609

Change-Id: I72d04b11f14fde25b7ad64e6a9a82f7c20e32b4c
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/284095
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>
diff --git a/package.json b/package.json
index 8076ae0..a6428c5 100644
--- a/package.json
+++ b/package.json
@@ -131,15 +131,6 @@
         "aliases": [
           "Go Checksum File"
-      },
-      {
-        "id": "tmpl",
-        "extensions": [
-          ".tmpl"
-        ],
-        "aliases": [
-          "Go Template File"
-        ]
     "grammars": [