Remove an unnecessary test dependency

This dependency probably has not been needed since revision
63f3303 removed
`com.ibm.wala.tests.util.SlowTests` as part of porting tests from JUnit
4 to JUnit 5.

build-logic/src/main/kotlin/com/ibm/wala/gradle/java.gradle.kts

@@ -108,7 +108,6 @@ tasks.named<Test>("test") {
 }
 
 if (hasProperty("excludeSlowTests")) {
-  dependencies { testImplementation(testFixtures(project(":core"))) }
   tasks.named<Test>("test") { useJUnitPlatform { excludeTags("slow") } }
 }