[K/N][Tests] Polish sharing_with_weak.kt

^KT-61259

compiler/testData/codegen/box/cinterop/objc/sharing_with_weak.kt

@@ -16,8 +16,6 @@ void setObject(NSObject* obj) {
     globalObject = obj;
 }
 
-// Make sure this function persists, because the test expects to find this function in the stack trace.
-__attribute__((noinline))
 bool isObjectAlive() {
     return globalObject != nil;
 }
@@ -30,8 +28,6 @@ import kotlin.test.*
 import kotlinx.cinterop.autoreleasepool
 import objclib.*
 
-val sb = StringBuilder()
-
 fun box(): String {
     val success = autoreleasepool {
         run()