Stop using yarn with extension pack (#14278)

* Use npm instead of yarn for the extension package vsix.

Author: sean-mcmanus

Build/package/jobs_package_vsix.yml

@@ -38,9 +38,6 @@ jobs:
     inputs:
       version: 22.x
 
-  - task: geeklearningio.gl-vsts-tasks-yarn.yarn-installer-task.YarnInstaller@3
-    displayName: Use Yarn 1.x
-
   - script: IF EXIST %SYSTEMDRIVE%\Users\%USERNAME%\.npmrc del %SYSTEMDRIVE%\Users\%USERNAME%\.npmrc
     displayName: Delete .npmrc if it exists
 
@@ -51,9 +48,9 @@ jobs:
       script: |
         export SRC_DIR=$(echo $BUILD_SOURCESDIRECTORY | sed 's|\\|/|g')
         cd "$SRC_DIR/${{ parameters.srcDir }}"
-        yarn install
+        npm install
         if [ $? -ne 0 ]; then
-          echo "yarn install failed, sleeping for 30s before retrying..."
+          echo "npm install failed, sleeping for 30s before retrying..."
           sleep 30
           exit 1
         fi