perf machine: Remove needless map_type from machine__load_vmlinux_path()

Since it uses machine__kernel_map() and this function always returns the
MAP__FUNCTION map, it doesn't make sense to call it with MAP__VARIABLE.

And also this is a step in the direction of nuking the MAP__{FUNCTION,VARIABLE}
split.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-0h3eof3kx3kq32ixg5fquf3p@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>