remove AfterBuild call to xbuild (#3128)

Xamarin.Forms.ControlGallery.Android/Xamarin.Forms.ControlGallery.Android.csproj

@@ -55,15 +55,6 @@
     <AndroidLinkMode>Full</AndroidLinkMode>
     <JavaMaximumHeapSize>1G</JavaMaximumHeapSize>
     <EmbedAssembliesIntoApk>True</EmbedAssembliesIntoApk>
-    <CustomCommands>
-      <CustomCommands>
-        <Command>
-          <type>AfterBuild</type>
-          <command>xbuild /t:SignAndroidPackage Xamarin.Forms.ControlGallery.Android/Xamarin.Forms.ControlGallery.Android.csproj</command>
-          <workingdir>${SolutionDir}</workingdir>
-        </Command>
-      </CustomCommands>
-    </CustomCommands>
     <AndroidSupportedAbis>armeabi;armeabi-v7a;x86</AndroidSupportedAbis>
     <Debugger>.Net (Xamarin)</Debugger>
     <DevInstrumentationEnabled>True</DevInstrumentationEnabled>