Perl was used to remove all the BTX and ETX markers from the code.
The specific command that was run on all "vtk*.h" files was this:
    perl -0777 -i -pe 's/(\n* *\/\/ *[BE]TX *\n+)+/\n\n/g'

This regex replaces each BTX/ETX line, plus any leading or trailing
blank lines, with a single blank line.