test_tickless: replacing depreciated APIs with new one.

As part of Zephyr release 1.9 some APIs will be depreciated. This patch
replaces two of such APIs (task_sleep(ticks), sys_tick_get_32()) with
new ones (k_sleep(ms), k_uptime_get_32()).

Jira: ZEP-2008

Change-Id: Ic0e05906dadfb2ddaea9d0a8b738294dc81430f9
Signed-off-by: Youvedeep Singh <youvedeep.singh@intel.com>