[test] eliminate a workaround made redundant by 49c5487

Author: glessard

test/Runtime/weak-reference-racetests-dispatch.swift

@@ -4,15 +4,6 @@
 // REQUIRES: objc_interop
 
 import StdlibUnittest
-
-// Also import modules which are used by StdlibUnittest internally. This
-// workaround is needed to link all required libraries in case we compile
-// StdlibUnittest with -sil-serialize-all.
-import SwiftPrivate
-#if _runtime(_ObjC)
-import ObjectiveC
-#endif
-
 import Dispatch
 
 let iterations = 200_000

test/Runtime/weak-reference-racetests.swift

@@ -3,14 +3,6 @@
 
 import StdlibUnittest
 
-// Also import modules which are used by StdlibUnittest internally. This
-// workaround is needed to link all required libraries in case we compile
-// StdlibUnittest with -sil-serialize-all.
-import SwiftPrivate
-#if _runtime(_ObjC)
-import ObjectiveC
-#endif
-
 let iterations = 1_000
 
 class Thing {}