btf: Remove AutoCloseable from BtfTrace

btf: Remove AutoCloseable from BtfTrace

Despite many great advantages, AutoCloseable does not work well
with subclasses of ITmfTrace, because it would imply that such
objects are not exposed publicly by other objects tracking them.

This is not the case in TMF, as many objects expose ITmfTrace's
through getters. Using instead TmfTrace's standard dispose()
method is more appropriate in subclasses.

Change-Id: I1d342d15dba7f8f6e75985f8aee6ed159838d424
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/51540
Reviewed-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>