Fix supporting array_equal for non-matching types/sizes

Here the goal is to simplify the expression for __CPROVER_array_equal
for things that are trivailly different, but we make it false = <complex
expression>, which leads the result to simply be non-deterministic

Author: Thomas Kiley

src/goto-symex/symex_other.cpp

@@ -240,7 +240,7 @@ void goto_symext::symex_other(
 
     // check for size (or type) mismatch
     if(array1.type() != array2.type())
-      assignment.lhs() = false_exprt();
+      assignment.rhs() = false_exprt();
 
     symex_assign(state, assignment);
   }