[Sema] test: fix linux smoke test

Author: hank121314

test/Sema/where_clause_across_module_boundaries.swift

@@ -6,7 +6,6 @@
 // Associated Type Inference fails across module boundaries
 // Self bounds from where clause cannot be accessed across modules.
 // This test is intended to test whether it can use generic signature to get self bounds.
-import Foundation
 import ModuleA
 
 struct ModuleBFoo: Codable, DefaultsSerializable {