[Java.Interop] Remove obj/* from @(Compile) for x-a (#585)

After commit 95712a2 we now hit the opposite condition:

The SDK-style build of `Java.Interop.csproj` generates
`obj/Release/netstandard2.0/.NETStandard,Version=v2.0.AssemblyAttributes.cs`
which is now included by the `<Compile Include="**\*.cs" />` within
`Java.Interop-MonoAndroid.csproj`.

Fix this by adding back the removal of `obj\**\**.cs` files.

Author: akoeplinger

src/Java.Interop/Java.Interop-MonoAndroid.csproj

@@ -52,6 +52,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="**\*.cs" />
+    <Compile Remove="obj\**\*.cs" />
     <Compile Remove="Tests\**\*.cs" />
     <Compile Remove="Java.Interop\JniLocationException.cs" />
   </ItemGroup>
@@ -104,4 +105,4 @@
     <None Include="Documentation\Java.Interop\JniManagedPeerStates.xml" />
     <None Include="Documentation\Java.Interop\JniEnvironment.References.xml" />
   </ItemGroup>
-</Project>
+</Project>