[$] Unexporting kallsyms_lookup_name()

One of the basic rules of kernel-module development is that modules canonly access symbols (functions and data structures) that have beenexplicitly exported. Even then, many symbols are restricted so that onlymodules with a GPL-compatible license can access them. It turns out,though, that there is a readily available workaround that makes it easy fora module to access any symbol it wants. That workaround seems likely to beremoved soon despite some possible inconvenience for some out-of-treeusers; the reason why that is happening turns out to be relativelyinteresting.