csdk: Relocate timerlib to c_common/octimer

csdk: Relocate timerlib to c_common/octimer

It never was an external library while it was located there,
the code is small enough to be part c_common utility library.

No functionnal changes were introduced, just reformated source.

Note, For Arduino, timer object is built using C++ compiler tricks,
that could be removed once support is dropped.

Bug: https://jira.iotivity.org/browse/IOT-1889
Change-Id: I776c5273315a7552495974f58a199a38073fb45e
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18009
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>