Debug: do not log memtrack_proc_get() failure

memtrack is an optional HAL, and memtrack_proc_get() will fail if
the HAL is not available on the device. Remove the warning to stop
flooding logcat every time read_memtrack_memory() is called.

Test: boot aosp_x86_64 and check logcat
Change-Id: I31b0e9bb3a881460bb4f2461dddb0e252763c609