Drop PRIORITY variable

As discussed on the mailing list, this variable isn't useful and if wanted
would be better implemented by distros using pn-X overrides.

This patch executes:

find . -regex ".*\.\(bb\|inc\)$" | xargs sed -i '/^PRIORITY = ".*"$/d'

against the tree removing the referenced. Thanks to Phil Blundell for
the command.

(From OE-Core rev: d122343362669c683acc4af295971a62cbc823fc)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/python/python-imaging_1.1.7.bb

@@ -1,6 +1,5 @@
 DESCRIPTION = "Python Imaging Library"
 SECTION = "devel/python"
-PRIORITY = "optional"
 LICENSE = "MIT"
 LIC_FILES_CHKSUM = "file://README;beginline=92;endline=120;md5=c4371af4579f1e489cf881c1443dd4ec"
 DEPENDS = "freetype jpeg tiff"