Deleted Perforce P4Merge 2020 (#11640)

Co-authored-by: Akinwale Alagbe <akalagbe@microsoft.com>

manifests/p/Perforce/P4Merge/2020.2/Perforce.P4Merge.yaml

@@ -1,27 +0,0 @@
-PackageIdentifier: Perforce.P4Merge
-PackageVersion: 2020.2
-PackageName: Helix Visual Merge Tool (P4Merge)
-Publisher: Perforce
-License: Copyright (c) Perforce Software, Inc.
-Moniker: p4merge
-Tags:
-- merge
-- diff
-- compare
-ShortDescription: Helix Visual Merge Tool (P4Merge) is a three-way merging and side-by-side file comparison tool. Use it to visualize your merges, obtain comprehensive file history, and compare a broad range of image files.
-PackageUrl: https://www.perforce.com/products/helix-core-apps/merge-diff-tool-p4merge
-Installers:
-- Architecture: x64
-  InstallerUrl: https://cdist2.perforce.com/perforce/r20.2/bin.ntx64/p4vinst64.exe
-  InstallerSha256: A049DC408549187D547DA3CB4B7386727F9EEF87E4DF452E7968F7FD571A88C9
-  InstallerType: exe
-  InstallerSwitches:
-    Silent: /silent
-    SilentWithProgress: /passive
-    Custom: REMOVEAPPS=P4ADMIN,P4V,P4
-    Interactive: ""
-    Log: /l <LOGPATH>
-    InstallLocation: INSTDIR=<INSTALLPATH>
-PackageLocale: en-US
-ManifestType: singleton
-ManifestVersion: 1.0.0