This patch removes includes that are not used. The removals were found with
include-what-you-use which checks if any of the symbols from a header is
in use.
In the process, rename udev_encode_string which is poorly named for what
it does. It deals specifically with encoding names that udev creates and
has its own rules: utf8 is valid but some ascii is not (e.g. path
separators), and everything else is simply escaped. Rename it to
encode_devnode_name.
