Remove JETBRAINS_ANNOTATIONS from project.

Terminal.Gui/Terminal.Gui.csproj

@@ -25,7 +25,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineTrace>true</DefineTrace>
     <DebugType>portable</DebugType>
-    <DefineConstants>$(DefineConstants);JETBRAINS_ANNOTATIONS;CONTRACTS_FULL;CODE_ANALYSIS</DefineConstants>
+    <DefineConstants>$(DefineConstants);CONTRACTS_FULL;CODE_ANALYSIS</DefineConstants>
     <ImplicitUsings>enable</ImplicitUsings>
     <NoLogo>true</NoLogo>
     <SuppressNETCoreSdkPreviewMessage>true</SuppressNETCoreSdkPreviewMessage>