bedtools: revert to v2.24.0
bedtools: revert to v2.24.0

bedtools v2.25.0 has a couple of problematic memory leaks not present in
v2.24.0:

https://github.com/arq5x/bedtools2/issues/302
https://github.com/arq5x/bedtools2/issues/303

This reverts the homebrew-science version back to 2.24.0 until Aaron and
Neil have a chance to release a new version.

Closes #2777.

Signed-off-by: Dominique Orban <b6b12199b0ff1342bf41262c4fcd3a561907b571@gmail.com>

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