.github/workflow: remove release.yml

Release is done from GCB.

Change-Id: If55e1f0a8b3a8e1bb866fd23cd35fa35c5f29acd
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/554315
Reviewed-by: Suzy Mueller <[email protected]>
TryBot-Result: kokoro <[email protected]>
Commit-Queue: Hyang-Ah Hana Kim <[email protected]>

Author: hyangah