Remove unnecessary definition of CancelRequested in bin/scripts/
This variable is now part of the refactored code for query cancellation
in fe_utils. This fixes an oversight in commit
a4fd3aa. While on it,
improve some header includes in bin/scripts/.
Author: Michael Paquier
Reviewed-by: Fabien Coelho
Discussion: https://postgr.es/m/
20191203101625.GF1634@paquier.xyz