Revert "[builds] Make the tools build use mono's packaged logic instead of our own."

[rolfbjarne]

Reverts #5962.

It breaks package creation:

[...]
Installing source files for Xamarin.iOS

Unhandled Exception:
System.IO.DirectoryNotFoundException: Could not find a part of the path "/Users/builder/jenkins/workspace/xamarin-macios/xamarin-macios/src/kspace/archive-mono/2019-02/ios/release/mcs/class/I18N/CJK/CP51932.cs".
  at System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.Boolean anonymous, System.IO.FileOptions options) [0x00164] in <b7d51802a4dc4818a2e8326fef769990>:0 
  at System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.IO.FileOptions options) [0x00000] in <b7d51802a4dc4818a2e8326fef769990>:0 
  at (wrapper remoting-invoke-with-check) System.IO.FileStream..ctor(string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare,int,System.IO.FileOptions)
  at System.IO.FileSystem.CopyFile (System.String sourceFullPath, System.String destFullPath, System.Boolean overwrite) [0x0001b] in <b7d51802a4dc4818a2e8326fef769990>:0 
  at System.IO.File.Copy (System.String sourceFileName, System.String destFileName, System.Boolean overwrite) [0x00062] in <b7d51802a4dc4818a2e8326fef769990>:0 
  at System.IO.File.Copy (System.String sourceFileName, System.String destFileName) [0x00000] in <b7d51802a4dc4818a2e8326fef769990>:0 
  at ListSourceFiles.Main (System.String[] arguments) [0x0069a] in <82f1054911124b7bb7f5819d369707fe>:0 

[monojenkins]

Build success
✅ Build succeeded
✅ API Diff (from stable)
⚠️ API Diff (from PR only) (🔥 breaking changes 🔥)
✅ Generator Diff (no change)
✅ Test run succeeded