Revert "refactored conditional jump generation to enable and/or generation"

This reverts commit b74bdb9cfd.

idea/testData/codegen/if.jet

@@ -0,0 +1 @@
+fun foo(b: Boolean): Int { return if (b) 15 else 20 }

idea/testData/codegen/singleBranchIf.jet

@@ -0,0 +1,4 @@
+fun foo(b: Boolean) : Int {
+  if (b) return 15;
+  return 20;
+}