Clean-up: remove extraneous "found" parameters in ust-elf

Clean-up: remove extraneous "found" parameters in ust-elf

In lttng-ust-elf.c, static functions used to extract build ID or debug
link information had an extraneous `found` parameter, carrying no more
information than could be obtained by checking the other out
parameters against NULL. The resulting simplified logic should also
prevent static analysis tools from misidentifying resource leaks.

Signed-off-by: Antoine Busque <abusque@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>