[Sema] Assert that we don't re-type-check conditions

Sink the assertion down into `TypeChecker::typeCheckCondition` and
remove the old logic.

Author: hamishknight

lib/Sema/TypeCheckConstraints.cpp

@@ -928,13 +928,7 @@ bool TypeChecker::typeCheckForEachPreamble(DeclContext *dc, ForEachStmt *stmt,
 }
 
 bool TypeChecker::typeCheckCondition(Expr *&expr, DeclContext *dc) {
-  // If this expression is already typechecked and has type Bool, then just
-  // re-typecheck it.
-  if (expr->getType() && expr->getType()->isBool()) {
-    auto resultTy =
-        TypeChecker::typeCheckExpression(expr, dc);
-    return !resultTy;
-  }
+  ASSERT(!expr->getType() && "the bool condition is already type checked");
 
   auto *boolDecl = dc->getASTContext().getBoolDecl();
   if (!boolDecl)

lib/Sema/TypeCheckStmt.cpp

@@ -865,7 +865,6 @@ static bool typeCheckHasSymbolStmtConditionElement(StmtConditionElement &elt,
 static bool typeCheckBooleanStmtConditionElement(StmtConditionElement &elt,
                                                  DeclContext *dc) {
   Expr *E = elt.getBoolean();
-  assert(!E->getType() && "the bool condition is already type checked");
   bool hadError = TypeChecker::typeCheckCondition(E, dc);
   elt.setBoolean(E);
   return hadError;