[hotfix][test] Use Long#compare to replace equivalent statements to improve readability.

Author: RocMarshal

flink-runtime/src/test/java/org/apache/flink/runtime/operators/hash/CompactingHashTableTest.java

@@ -70,7 +70,7 @@ public boolean equalToReference(Tuple2<Long, String> candidate) {
                     public int compareToReference(Tuple2<Long, String> candidate) {
                         long x = ref;
                         long y = candidate.f0;
-                        return (x < y) ? -1 : ((x == y) ? 0 : 1);
+                        return Long.compare(x, y);
                     }
                 };
     }

flink-runtime/src/test/java/org/apache/flink/runtime/operators/hash/HashTableTest.java

@@ -99,7 +99,7 @@ public boolean equalToReference(Tuple2<Long, byte[]> candidate) {
                     public int compareToReference(Tuple2<Long, byte[]> candidate) {
                         long x = ref;
                         long y = candidate.f0;
-                        return (x < y) ? -1 : ((x == y) ? 0 : 1);
+                        return Long.compare(x, y);
                     }
                 };
     }

flink-runtime/src/test/java/org/apache/flink/runtime/operators/hash/InPlaceMutableHashTableTest.java

@@ -118,7 +118,7 @@ public boolean equalToReference(Tuple2<Long, String> candidate) {
                     public int compareToReference(Tuple2<Long, String> candidate) {
                         long x = ref;
                         long y = candidate.f0;
-                        return (x < y) ? -1 : ((x == y) ? 0 : 1);
+                        return Long.compare(x, y);
                     }
                 };
     }

flink-tests/src/test/java/org/apache/flink/test/manual/HashTableRecordWidthCombinations.java

@@ -83,7 +83,7 @@ public boolean equalToReference(Tuple2<Long, byte[]> candidate) {
                     public int compareToReference(Tuple2<Long, byte[]> candidate) {
                         long x = ref;
                         long y = candidate.f0;
-                        return (x < y) ? -1 : ((x == y) ? 0 : 1);
+                        return Long.compare(x, y);
                     }
                 };