Fix Avalonia.Input.UnitTests.csproj

Previously this project was spewing loads of

```
Severity	Code	Description	Project	File	Line	Suppression State
Warning	CS1701	Assuming assembly reference 'System.Runtime, Version=4.0.20.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' used by 'Avalonia.Controls' matches identity 'System.Runtime, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' of 'System.Runtime', you may need to supply runtime policy	Avalonia.Input.UnitTests(net461)	D:\projects\Avalonia\tests\Avalonia.Input.UnitTests\CSC	1	Active`
```

Warnings. Not sure why this was, but updating the `csproj` to be in the same format as the other unit tests stops these warnings and reduces the warnings for a solution build from 5755(!) to 238.

tests/Avalonia.Input.UnitTests/Avalonia.Input.UnitTests.csproj

@@ -3,35 +3,6 @@
     <TargetFrameworks>net461;netcoreapp1.1</TargetFrameworks>
     <OutputType>Library</OutputType>
   </PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
-    <DebugSymbols>true</DebugSymbols>
-    <DebugType>full</DebugType>
-    <Optimize>false</Optimize>
-    <OutputPath>bin\Debug\</OutputPath>
-    <DefineConstants>DEBUG;TRACE</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <DocumentationFile>bin\Debug\Avalonia.Input.UnitTests.XML</DocumentationFile>
-    <NoWarn>CS1591</NoWarn>
-  </PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <DebugType>pdbonly</DebugType>
-    <Optimize>true</Optimize>
-    <OutputPath>bin\Release\</OutputPath>
-    <DefineConstants>TRACE</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-  </PropertyGroup>
-  <ItemGroup>
-    <Reference Include="System" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.Xml.Linq" />
-    <Reference Include="System.Data.DataSetExtensions" />
-    <Reference Include="Microsoft.CSharp" />
-    <Reference Include="System.Data" />
-    <Reference Include="System.Xml" />
-    <Reference Include="WindowsBase" />
-  </ItemGroup>
   <Import Project="..\..\build\UnitTests.NetCore.targets" />
   <Import Project="..\..\build\Moq.props" />
   <Import Project="..\..\build\XUnit.props" />
@@ -49,6 +20,6 @@
     <ProjectReference Include="..\Avalonia.UnitTests\Avalonia.UnitTests.csproj" />
   </ItemGroup>
   <ItemGroup>
-    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+    <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
   </ItemGroup>
-</Project>
+</Project>