Disable VSTS clean. (#20248)

* Disable VSTS clean.
We have our own clean script that we run and is more reliable.

* Change Linux Crossbuild to not clean to match the non-Crossbuild definition.

buildpipeline/DotNet-CoreFx-Trusted-Linux-Crossbuild.json

@@ -459,7 +459,7 @@
     "name": "DotNet-CoreFX-Trusted",
     "url": "https://devdiv.visualstudio.com/DevDiv/_git/DotNet-CoreFX-Trusted",
     "defaultBranch": "refs/heads/master",
-    "clean": "true",
+    "clean": "false",
     "checkoutSubmodules": false
   },
   "quality": "definition",

buildpipeline/DotNet-CoreFx-Trusted-OSX.json

@@ -270,9 +270,6 @@
     "PB_VsoCorefxGitUrl": {
       "value": "https://github.com/dotnet/corefx"
     },
-    "Build.Clean": {
-      "value": "all"
-    },
     "PB_BuildArguments": {
       "value": "-buildArch=x64 -Release",
       "allowOverride": true

buildpipeline/DotNet-CoreFx-Trusted-Windows-NoTest.json

@@ -331,9 +331,6 @@
       "value": "HEAD",
       "allowOverride": true
     },
-    "Build.Clean": {
-      "value": "all"
-    },
     "PB_VsoAccountName": {
       "value": "dn-bot"
     },

buildpipeline/DotNet-CoreFx-Trusted-Windows.json

@@ -385,9 +385,6 @@
       "value": "HEAD",
       "allowOverride": true
     },
-    "Build.Clean": {
-      "value": "all"
-    },
     "PB_VsoAccountName": {
       "value": "dn-bot"
     },