Fix: error: remove trailing period from error descriptions

Fix: error: remove trailing period from error descriptions

Trailing periods in some error descriptions cause the client to print
two dots at the end of some error messages:

Error: Failed to register trigger: Tracing the kernel requires a root
lttng-sessiond daemon, as well as "tracing" group membership or root
user ID for the lttng client..

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ib6522252fb716b1baad3c7416e2db150c614702c