Implement general expresion remover

idea/testData/codeInsight/unwrapAndRemove/removeExpression/ifInBlock.kt

@@ -0,0 +1,10 @@
+// OPTION: 0
+fun foo(n : Int): Int {
+    <caret>if (n > 0) {
+        1
+    } else {
+        -1
+    }
+
+    return 0
+}