core: cleanup task boost list

Cleanup entries in the task boost list when the pid becomes inactive.

Change-Id: I0b1b2ef81cda470cd08b31ab4e78f81d346b9b70
Acked-by: Ryan Chapman <rchapman@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>