libdlog: remove library destructor

libdlog: remove library destructor

A destructor assumes that it has an exclusive thread
access (no other library function can run in paralell).
This condition is not always met, which can lead to a
race condition and use after free situation. Since all
other, backend specific resources are not freed anyway,
we can get rid of the destructor to make things more
reliable.
The function itself is left because it is still necessary
in tests.

Change-Id: I3bc2a7b660c6c805182592a70a8a954beba16772
Signed-off-by: Maciej Slodczyk <m.slodczyk2@partner.samsung.com>