value-pairs: Fix a heavy memory leak

Due to a cherry pick that went wrong, when value-pairs was splitting up
the dot-notation into components, each component was mistakenly
strdup()'d twice. The fix was to remove the stray duplication, that
should have been removed when resolving the cherry-pick conflict.

This closes #183.

Reported-by: Fabien Wernli
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>