Fix SyncProjects.exe to avoid empty <ItemGroup /> propagation.

Author: yfakariya

src/MsgPack.Xamarin.Android/MsgPack.Xamarin.Android.csproj

@@ -679,7 +679,6 @@
     </Compile>
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
-  <ItemGroup />
   <ItemGroup>
     <None Include="..\MsgPack\remarks.xml">
       <Link>remarks.xml</Link>

test/MsgPack.UnitTest.Xamarin.Android/MsgPack.UnitTest.Xamarin.Android.csproj

@@ -60,7 +60,6 @@
       <Name>MsgPack.Xamarin.Android</Name>
     </ProjectReference>
   </ItemGroup>
-  <ItemGroup />
   <ItemGroup>
     <None Include="..\..\src\MsgPack.snk">
       <Link>MsgPack.snk</Link>

tools/SyncProjects/SyncProjects/Program.cs

@@ -165,15 +165,13 @@ private static void SynchronizeProjects( string syncFilePath, string sourceBaseP
 					}
 				}
 
+				// Avoid empty ItemGroups
+				projectXml.Root.Elements( Ns + "ItemGroup" ).Where( ig => !ig.HasElements ).Remove();
+
 				projectXml.Save( projectFilePath );
 			}
 		}
 
-		private static IEnumerable<ItemGroup> ToItemGroups( XContainer projectXml )
-		{
-			return projectXml.Elements( Ns + "ItemGroup" ).Select( e => new ItemGroup( e ) );
-		}
-
 		private static void CopyItemGroup( string elementName, IEnumerable<XElement> sourceItems, XElement destinationItemGroup, string relativePath, IEnumerable<string> includings, IEnumerable<string> excludings, IEnumerable<string> preservings )
 		{
 			var remaining =