Remove MSProxy support

It's not enabled anywhere, certainly not maintained

src/common/common.vcxproj

@@ -26,7 +26,6 @@
     <ClInclude Include="inet.h" />
     <ClInclude Include="marshal.h" />
     <ClInclude Include="modes.h" />
-    <ClInclude Include="msproxy.h" />
     <ClInclude Include="network.h" />
     <ClInclude Include="notify.h" />
     <ClInclude Include="outbound.h" />
@@ -59,7 +58,6 @@
     <ClCompile Include="inbound.c" />
     <ClCompile Include="marshal.c" />
     <ClCompile Include="modes.c" />
-    <ClCompile Include="msproxy.c" />
     <ClCompile Include="network.c" />
     <ClCompile Include="notify.c" />
     <ClCompile Include="outbound.c" />
@@ -167,4 +165,4 @@ powershell -File "$(SolutionDir)..\win32\version-template.ps1" "$(SolutionDir)..
       ]]></Command>
     </PreBuildEvent>
   </ItemDefinitionGroup>
-</Project>
+</Project>