pgsql: Remove unnecessary definition of CancelRequested in bin/scripts/

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

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/85b9ef5fe7533e5d07dcf2a2b67c8855a34e5125

Modified Files
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src/bin/scripts/clusterdb.c        | 1 +
src/bin/scripts/common.c           | 1 +
src/bin/scripts/common.h           | 3 ---
src/bin/scripts/reindexdb.c        | 1 +
src/bin/scripts/scripts_parallel.c | 1 +
src/bin/scripts/vacuumdb.c         | 1 +
6 files changed, 5 insertions(+), 3 deletions(-)