Revert merge.targets and add package .targets file to remove proto dependency

Co-authored-by: jonathanpeppers <840039+jonathanpeppers@users.noreply.github.com>

Author: Copilot

source/androidx.health.connect/connect-client/Xamarin.AndroidX.Health.Connect.Client.targets

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <!-- Remove the proto package reference as proto classes are embedded in this package -->
+    <PackageReference Remove="Xamarin.AndroidX.Health.Connect.Client.Proto" />
+  </ItemGroup>
+</Project>