[cxx-interop] Remove remnants of symbolic import mode

Symbolic import mode was removed in b51cfa5. This removes a reference to it from a test.

Author: egorzhdan

test/Interop/Cxx/class/inheritance/circular-inheritance-typechecker.swift

@@ -1,8 +1,4 @@
-// RUN: %empty-directory(%t/index)
-// RUN: %target-typecheck-verify-swift -verify-ignore-unknown -I %S/Inputs -cxx-interoperability-mode=default -index-store-path %t/index
-//
-// Note that we specify an -index-store-path to ensure we also test importing symbolic C++ decls,
-// to exercise code that handles importing unspecialized class templates.
+// RUN: %target-typecheck-verify-swift -verify-ignore-unknown -I %S/Inputs -cxx-interoperability-mode=default
 
 import CircularInheritance