Remove unnecessary include of

Remove unnecessary include of 

This was probably never necessary.  (The header used to use random(),
but that shouldn't require  either.  In any case, that's gone,
too.)

Reviewed-by: Shubham Khanna 
Reviewed-by: Tom Lane 
Discussion: https://www.postgresql.org/message-id/flat/cff5475d-e0a9-4561-b094-794aa36bd031%40eisentraut.org