remove the unneeded header file math.h in binaryheap.c - Mailing list pgsql-hackers

Hi Hackers,

I found in file binaryheap.c， file "math.h" was included, but it is uncessary, so I removed it 

and filing a patch to address the issue.

I have verified that, build is OK.

Please see the attachment and help review it.

thanks a lot!

liujinyang