User Story 37545: Create app context switch test helper

- Fixed net462 compile error.

Author: paulmedynski

src/Microsoft.Data.SqlClient/tests/Common/LocalAppContextSwitchesHelper.cs

@@ -143,7 +143,6 @@ void InitField(string name, out FieldInfo field, out Tristate value)
 
 #if NETFRAMEWORK
         InitField(
-            switchesType,
             "s_disableTNIRByDefault",
             out _disableTNIRByDefaultField,
             out _disableTNIRByDefaultOriginal);