Exclude histogram headers in LHCb ref preprocessor

With !2260 (merged) counter and histogram summary tables are appended explicitly to preprocessed references to create new refs. Histogram header lines were not filtered by the preprocessor, which leads to them appearing twice in the new refs, which in turn makes the new refs invalid. This MR fixes that by extending the list of exclusions.

added bug fix lhcb-head testing labels

@jonrob this is the fix to go with !2260 (merged). Once merged you need to remake the ref update that goes with !2265 (merged)

• [2019-12-24 00:05] Validation started with lhcb-head#2472
• [2019-12-30 00:06] Validation started with lhcb-head#2473
• [2020-01-06 00:10] Validation started with lhcb-head#2474

resolved all threads

removed lhcb-head label

merged

mentioned in commit 44ebfde9

added backport run2 label

mentioned in merge request Brunel!928 (merged)

mentioned in commit Brunel@cbca52fe

mentioned in merge request Brunel!931 (merged)

mentioned in commit Moore@a1d3fade

mentioned in merge request Moore!357 (merged)

mentioned in issue Moore#128 (closed)

added Build label and removed testing label

mentioned in commit a4efaeb0