libtraceevent: Remove tep_register_trace_clock()

The tep_register_trace_clock() API is used to instruct the traceevent
library how to print the event time stamps. As event print interface if
redesigned, this API is not needed any more.  The new event print API is
flexible and the user can specify how the time stamps are printed.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Patrick McLean <chutzpah@gentoo.org>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/linux-trace-devel/20190801074959.22023-3-tz.stoyanov@gmail.com
Link: http://lore.kernel.org/lkml/20190805204355.195042846@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>