tmf: Drop the Type in CtfTmfTimestamp

tmf: Drop the Type in CtfTmfTimestamp

Also removed all redundant methods in the class and the test.
This brings CtfTmfTimestamp much closer to TmfTimestamp, now
it's simply a wrapper that ensures the scale is set to nanoseconds.

Change-Id: I8242434af7221ae1d6dd964d5c8d80cd0f4e60bc
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/8047
Tested-by: Hudson CI
Reviewed-by: Francois Chouinard <fchouinard@gmail.com>
IP-Clean: Francois Chouinard <fchouinard@gmail.com>
Tested-by: Francois Chouinard <fchouinard@gmail.com>