NFD

Steps to reproduce:

1. run NFD and have traffic go through it
2. observe nNameTreeEntries, nFibEntries, nPitEntries, nMeasurementsEntries counters over time

Expected: nNameTreeEntries is linear with (nFibEntries + nPitEntries + nMeasurementsEntries)

Actual: nNameTreeEntries is constantly growing over time

At one instance, after NFD runs for 8748 seconds, the counters are:
nNameTreeEntries=69618, nFibEntries=6, nPitEntries=16, nMeasurementsEntries=76

There are at most 98 leaf nodes on the NameTree.
In the worst case that all Names are disjoint, the average Name length would be 710 Components, which is far from the expected traffic pattern.

Therefore I conclude there is a memory leak on the usage of NameTree: when a FIB/PIT/Measurements entry is erased, the corresponding NameTree entry (if empty) isn't erased.