A ridiculously fast way of doing this is:

for i in $(pcregrep -l -M -r --include='.*[hc]xx$' \
  --exclude-dir=workdir --exclude-dir=instdir '^
{3,}' .)
do
    perl -0777 -i -pe 's/^
{3,}/

/gm' $i
done

Change-Id: Iebb93eccbee9e4fc5c4380474ba595858a27ac2c
Reviewed-on: https://gerrit.libreoffice.org/22224Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>