[release.theia] package.json: run npm dedupe

Duplicated package dependency was found and vsce package was unhappy.

For #1038

Change-Id: I10cb6ec1cf72bd163cdb5fde730c000b836506e7
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/278790
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: Rebecca Stambler <rstambler@golang.org>

Author: hyangah

package-lock.json

@@ -58,7 +58,6 @@
     "vscode-debugadapter-testsupport": "^1.42.0",
     "vscode-debugprotocol": "^1.40.0",
     "vscode-languageclient": "6.1.3",
-    "vscode-languageserver-protocol": "3.15.3",
     "web-request": "^1.0.7"
   },
   "devDependencies": {