(GH-9) Removed code that is not required

- Based on the original work by Particular, there were some classes, and
hence tests, that are not required, lets remove them to make the code
easier to understand and maintain.

Author: gep13

src/Compiler/ReleaseManager.cs

@@ -57,10 +57,8 @@
     <Compile Include="AssemblyInfo.cs" />
     <Compile Include="DefaultGitHubClient.cs" />
     <Compile Include="IGitHubClient.cs" />
-    <Compile Include="ReleaseManager.cs" />
     <Compile Include="ReleaseNotesBuilder.cs" />
     <Compile Include="OctokitExtensions.cs" />
-    <Compile Include="ReleaseUpdateRequired.cs" />
     <Compile Include="MilestoneExtensions.cs" />
   </ItemGroup>
   <ItemGroup>

src/Compiler/ReleaseNotesCompiler.csproj

@@ -61,7 +61,6 @@
     <Compile Include="ClipBoardHelper.cs" />
     <Compile Include="FakeGitHubClient.cs" />
     <Compile Include="Helper.cs" />
-    <Compile Include="ReleaseManagerTests.cs" />
     <Compile Include="ReleaseNotesBuilderIntegrationTests.cs" />
     <Compile Include="ClientBuilder.cs" />
     <Compile Include="ReleaseNotesBuilderTests.cs" />