Remove obsolete warning from restorecon_recursive documentation.

We originally included a warning to not invoke restorecon_recursive
with a path leading to a shell-writable or app-writable directory
due to concerns about the potential for mischief with symlinks during
the restorecon_recursive.  However, this warning was never necessary for
calling restorecon_recursive during system initialization before an adb
shell or app can run, and we have further prohibited init from
reading/following symlinks that can be created by shell or apps in
policy, so this warning is superfluous.  It also contradicts current
usage of restorecon_recursive in rootdir/init.rc, since it is called
there on /data.

Change-Id: I28a635e0b5991ced8adcef93e7a04f9d9e5634fd
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>