Fixing a problem with dh/dl 1-4 interactions

In some cases, dh/dl interactions are added twice when the
couple-intermol keyword is not used.

These lines were originally removed in 7763fa8f while fixing thread
safety in free-energy calculations, but were erroneously re-introduced
in f40969c. Versions 4.6 and 4.6.1 were affected.

Fixes #1225

Change-Id: If24177833eb4a96a6c6ef0d1ecc9a23bf80a90b1
Merge "Fixing a problem with dh/dl 1-4 interactions" into release-4-6