gopls/release: remove unused(?) script

It confuses me whenever I look for doc/release/*.md and
appears not to have been touched in a long time.

Change-Id: I101577e75e884ace46e0fc49d550ada1036237e9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/622175
Auto-Submit: Alan Donovan <[email protected]>
Reviewed-by: Hongxiang Jiang <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: adonovan