dfa: make state merging result predictable

when removing a!=b and a!=c && b==c, don't restore a!=c

java/java-tests/testData/inspection/dataFlow/fixture/DontMakeUnrelatedVariableFalseWhenMerging.java

@@ -0,0 +1,26 @@
+import org.jetbrains.annotations.Nullable;
+
+import java.io.File;
+
+class Some {
+  void foo(String[] args) {
+    boolean b = false;
+
+    if (hashCode() == 2) {
+      b = new File("a").exists();
+    }
+
+    boolean b2 = hashCode() == 4;
+    if (!b2) {
+      return;
+    }
+
+    if (b) {
+
+    }
+
+    if (b) {
+
+    }
+  }
+}