Remove unnecessary include of <math.h>

Remove unnecessary include of <math.h>

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

Reviewed-by: Shubham Khanna <Shubham.Khanna@fujitsu.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/cff5475d-e0a9-4561-b094-794aa36bd031%40eisentraut.org