Redundant parameter in the get_useful_pathkeys_for_relation

Hi,

Working on an unrelated project, I found that the 
get_useful_pathkeys_for_relation routine has redundant parameter 
'require_parallel_safe'. This routine is static and is called only once 
with the 'true' value. Hence, it is evident that this parameter is a 
redundant one. The thread [1] seems not to explain why it is necessary. 
Although this function may be reused someday, I propose to remove this 
parameter or, at least, clarify why it is required here.
I would also remove the same parameter from the interface of routine 
relation_can_be_sorted_early, but it is exported, and someone may 
already use it in a loadable module.

See the patch attached.

[1] 
https://www.postgresql.org/message-id/flat/CAAaqYe8cK3g5CfLC4w7bs%3DhC0mSksZC%3DH5M8LSchj5e5OxpTAg%40mail.gmail.com

-- 
regards, Andrei Lepikhov