toaster: fix broken reference to urllib

toaster: fix broken reference to urllib

The code previously imported urllib to make use of querystring
quoting, but was modified to support Python 3. During this
process, the reference to urllib was not fixed, which resulted
in table filters breaking.

Remove the reference to urllib (which is no longer imported)
and instead reference the imported unquote_plus() function.

Signed-off-by: Elliot Smith <elliot.smith@intel.com>
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>