selftests/ftrace: Remove trigger-extended-error-support testcase

Error handling has been moved to the common tracing/error_log, so this
test is no longer valid.

Link: http://lkml.kernel.org/r/876a98b21018814cbf46f0a3605ae0906c51d53c.1554072478.git.tom.zanussi@linux.intel.com

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>