HPCC-11000 Update numFilesToProcess when removing a file from todo

Incorrect NumFilesToProcess is found in ESP Roxie metrics. This fix
decrements the numFilesToProcess when removing a file from todo queue.
Merge pull request #5523 from wangkx/h11000a

HPCC-11000 Update numFilesToProcess when removing a file from todo

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>