Remove kallsyms_lookup_name() wrapper

Remove kallsyms_lookup_name() wrapper

After the removable of get_vmalloc_info(), the unused global memory
variables, and the optional dcache/icache shrinkers there is no
longer a need for the kallsyms compatibility code.  This allows
us to eliminate another brittle area of the code by removing the
kernel upcall this functionality depended on for older kernels.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>