Revert "Allow simple R-assign in endless def"

This reverts commit 67bcac8.

parse.y

@@ -1104,7 +1104,7 @@ static int looking_at_eol_p(struct parser_params *p);
 %type <node> string_contents xstring_contents regexp_contents string_content
 %type <node> words symbols symbol_list qwords qsymbols word_list qword_list qsym_list word
 %type <node> literal numeric simple_numeric ssym dsym symbol cpath def_name defn_head defs_head
-%type <node> top_compstmt top_stmts top_stmt begin_block rassign arg_rassign
+%type <node> top_compstmt top_stmts top_stmt begin_block rassign
 %type <node> bodystmt compstmt stmts stmt_or_begin stmt expr arg primary command command_call method_call
 %type <node> expr_value expr_value_do arg_value primary_value fcall rel_expr
 %type <node> if_tail opt_else case_body case_args cases opt_rescue exc_list exc_var opt_ensure
@@ -1195,7 +1195,6 @@ static int looking_at_eol_p(struct parser_params *p);
 
 %nonassoc tLOWEST
 %nonassoc tLBRACE_ARG
-%left tASSOC
 
 %nonassoc  modifier_if modifier_unless modifier_while modifier_until keyword_in
 %left  keyword_or keyword_and
@@ -1537,19 +1536,6 @@ rassign 	: arg_value tASSOC lhs
 		    }
 		;
 
-arg_rassign	: arg tASSOC lhs %prec tLOWEST
-		    {
-		    /*%%%*/
-			$$ = node_assign(p, $3, $1, &@$);
-		    /*% %*/
-		    /*% ripper: assign!($3, $1) %*/
-		    }
-		| arg %prec tLOWEST
-		    {
-			$$ = $1;
-		    }
-		;
-
 command_asgn	: lhs '=' command_rhs
 		    {
 		    /*%%%*/
@@ -2459,7 +2445,7 @@ arg		: lhs '=' arg_rhs
 		    /*% %*/
 		    /*% ripper: ifop!($1, $3, $6) %*/
 		    }
-		| defn_head f_arglist_opt '=' arg_rassign
+		| defn_head f_arglist_opt '=' arg
 		    {
 			restore_defun(p, $<node>1->nd_defn);
 		    /*%%%*/
@@ -2468,7 +2454,7 @@ arg		: lhs '=' arg_rhs
 		    /*% ripper: def!(get_value($1), $2, $4) %*/
 			local_pop(p);
 		    }
-		| defs_head f_arglist_opt '=' arg_rassign
+		| defs_head f_arglist_opt '=' arg
 		    {
 			restore_defun(p, $<node>1->nd_defn);
 		    /*%%%*/

test/ruby/test_syntax.rb

@@ -1419,7 +1419,6 @@ def test_methoddef_endless
     assert_valid_syntax('private def inc(x) = x + 1')
     assert_valid_syntax('private def obj.foo = 42')
     assert_valid_syntax('private def obj.inc(x) = x + 1')
-    assert_valid_syntax('private def obj.inc(x) = x + 1 => @x')
   end
 
   def test_methoddef_in_cond