trace: ipc_logging: Destroy debugfs directories with logging contexts

IPC Logging currently creates debugfs directories for each of its
logging contexts, but does not remove them when destroying the contexts.
If a user attempts to access a directory associated with a destroyed
context, a crash will result.

Destroy debugfs directories when the logging context is destroyed.

Change-Id: I5a3b1cbf2fb5d9d0ede3d9da0fccd605b9fdf619
Signed-off-by: Steven Cahail <scahail@codeaurora.org>