CI: Don't upgrade npm twice on Windows

Author: DeeDeeG

script/vsts/platforms/templates/bootstrap.yml

@@ -2,7 +2,7 @@ steps:
   - pwsh: |
       # OS specific env variables
       if ($env:AGENT_OS -eq "Windows_NT") {
-        $env:NPM_BIN_PATH="C:/hostedtoolcache/windows/node/12.4.0/x64/npm.cmd"
+        $env:NPM_BIN_PATH="C:/npm/prefix/npm.cmd"
         $env:npm_config_build_from_source=true
       }
       if ($env:AGENT_OS -eq "Darwin") {

script/vsts/platforms/templates/preparation.yml

@@ -42,18 +42,6 @@ steps:
       versionSpec: '3.8'
     condition: eq(variables['Agent.OS'], 'Windows_NT')
 
-  - script: |
-      ECHO Installing npm-windows-upgrade
-      npm install --global --production npm-windows-upgrade
-    displayName: Install npm-windows-upgrade
-    condition: eq(variables['Agent.OS'], 'Windows_NT')
-
-  - script: |
-      ECHO Upgrading npm
-      npm-windows-upgrade --no-spinner --no-prompt --npm-version 6.14.8
-    displayName: Install npm 6.14.8
-    condition: eq(variables['Agent.OS'], 'Windows_NT')
-
   - script: |
       cd script\vsts
       npm install