all: remove it smartcast and replace with original variable name (#5764)

vlib/v/ast/ast.v

@@ -389,13 +389,13 @@ pub fn (i &Ident) var_info() IdentVar {
 
 pub struct InfixExpr {
 pub:
-	op         token.Kind
-	pos        token.Position
-	left       Expr
-	right      Expr
+	op           token.Kind
+	pos          token.Position
+	left         Expr
+	right        Expr
 pub mut:
-	left_type  table.Type
-	right_type table.Type
+	left_type    table.Type
+	right_type   table.Type
 }
 
 pub struct PostfixExpr {
@@ -443,6 +443,7 @@ pub:
 	comments []Comment
 pub mut:
 	smartcast bool // should only be true if cond is `x is sumtype`, it will be set in checker - if_expr
+	left_as_name string // only used in x is SumType check
 }
 
 pub struct LockExpr {

vlib/v/ast/str.v

@@ -279,7 +279,7 @@ pub fn (node Stmt) str() string {
 			mut out := ''
 			for i, left in it.left {
 				if left is Ident {
-					var_info := it.var_info()
+					var_info := left.var_info()
 					if var_info.is_mut {
 						out += 'mut '
 					}