fix clean script for the example applications (#16767)

running npm run clean failed as the example applications did not call the correct theiaext clean

Author: ndoschek

examples/browser-only/package.json

@@ -72,7 +72,7 @@
   },
   "scripts": {
     "prepare:no-native": "lerna run prepare --scope=\"@theia/re-exports\" && lerna run generate-theia-re-exports --scope=\"@theia/core\"",
-    "clean": "theia clean",
+    "clean": "theiaext clean",
     "build": "theiaext build && npm run -s bundle",
     "bundle": "theia build --mode development",
     "compile": "theiaext compile",

examples/browser/package.json

@@ -97,7 +97,7 @@
     "@theia/workspace": "1.67.0"
   },
   "scripts": {
-    "clean": "theia clean",
+    "clean": "theiaext clean",
     "build": "theiaext build && npm run -s bundle",
     "build:production": "theiaext build && npm run -s bundle:production",
     "bundle": "npm run rebuild && theia build --mode development",

examples/electron/package.json

@@ -103,7 +103,7 @@
   "scripts": {
     "build": "theiaext build && npm run -s bundle",
     "bundle": "npm run rebuild && theia build --mode development",
-    "clean": "theia clean",
+    "clean": "theiaext clean",
     "compile": "tsc -b",
     "lint": "theiaext lint",
     "rebuild": "theia rebuild:electron --cacheRoot ../..",