CI: Don't upgrade npm twice on Windows

We already install the npm version we want in previous steps

#140

Author: aminya

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/12.16.3/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

@@ -34,18 +34,6 @@ 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 6.9.0
-    displayName: Install npm 6.9.0
-    condition: eq(variables['Agent.OS'], 'Windows_NT')
-
   - script: |
       npm install --global --production [email protected]
     displayName: Install windows build tools