Remove definition of JUMBLE_SIZE from queryjumble.h
The same exists in queryjumble.c, and it is used only locally in this
file so let's remove the definition in the header.
Author: Tatsu Nakamori
Reviewed-by: Tom Lane, Julien Rouhaud
Discussion: https://postgr.es/m/
bb4ebd0412da9b1ac87a5eb2a3646bf1@oss.nttdata.com