qseecom: Fix issues with qssecom_remove/exit APIs

Clean-up the qseecom_remove() function by removing the null pointer
dereference. Change the logic by removing the unnecessary code and
also modified the qseecom_exit() function with proper calls.

Change-Id: Ibcca1b3c2c37024661505de2550e202b507703aa
Signed-off-by: AnilKumar Chimata <anilc@codeaurora.org>