Forbid "=& new" in PHP 7 mode

Author: nikic

grammar/php7.y

@@ -512,7 +512,6 @@ expr:
     | list_expr '=' expr                                    { $$ = Expr\Assign[$1, $3]; }
     | variable '=' expr                                     { $$ = Expr\Assign[$1, $3]; }
     | variable '=' '&' variable                             { $$ = Expr\AssignRef[$1, $4]; }
-    | variable '=' '&' new_expr                             { $$ = Expr\AssignRef[$1, $4]; }
     | new_expr                                              { $$ = $1; }
     | T_CLONE expr                                          { $$ = Expr\Clone_[$2]; }
     | variable T_PLUS_EQUAL expr                            { $$ = Expr\AssignOp\Plus      [$1, $3]; }