vscode-go: a few small clean-up items

Delete the merge.bash file as we no longer need it.
Fix a Markdown lint warning in SECURITY.md.
Mention linting in the contribution doc.
Delete outdated CONTRIBUTING.md.

Change-Id: Ica9afdfb3a4f906df890c7dddf3740bdad8f44da
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/237257
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>

Author: stamblerre

CONTRIBUTING.md

@@ -2,4 +2,4 @@
 
 ## Reporting a Vulnerability
 
-See https://golang.org/security for how to report a vulnerability.
+See [golang.org/security](https://golang.org/security) to report a vulnerability.

SECURITY.md

@@ -44,6 +44,10 @@ Please note that extra configuration is required to build and run the [Debug Ada
 
 3) Make sure the `window.openFoldersInNewWindow` setting is not `"on"`.
 
+#### Lint
+
+You can run `npm run lint` on the command-line to check for lint errors in your program. You can also use the [TSLint](https://marketplace.visualstudio.com/items?itemName=ms-vscode.vscode-typescript-tslint-plugin) plugin to see errors as you code.
+
 ### Run
 
 To run the extension with your patch, open the Run view (`Ctrl+Shift+D`), select `Launch Extension`, and click the Play button (`F5`).