debug: tracing: Remove unneeded abstraction

Various C and Assembly modules
make function calls to z_sys_trace_*. These merely call
corresponding functions sys_trace_*. This commit
is to simplify these by making direct function calls
to the sys_trace_* functions from these modules.
Subsequently, the z_sys_trace_* functions are removed.

Signed-off-by: Mrinal Sen <msen@oticon.com>