Revert what looks like an accidental edit

It appears to have been benign for now, but I worry about it...

Author: airbreather

ProjNet/ProjNET.csproj

@@ -7,7 +7,6 @@
     <TargetFrameworks>net35-client;net40-client;net403-client;net45;netstandard1.0;netstandard2.0</TargetFrameworks>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>$(SolutionDir)scskey.snk</AssemblyOriginatorKeyFile>
-    <TargetFramework>net35</TargetFramework>
   </PropertyGroup>
 
   <Import Project="$(SolutionDir)ProjNet.Common.props" />