[checkbox-ce-oem] Remove manifest from resource job (BugFix) (#1316)

Remove manifest from resource job

To prevent the issue of get empty manifest in very first run of checkbox test

contrib/checkbox-ce-oem/checkbox-provider-ce-oem/units/gpio/jobs.pxu

@@ -27,9 +27,7 @@ _description:
 estimated_duration: 0.02
 imports:
   from com.canonical.certification import lsb
-  from com.canonical.plainbox import manifest
 requires:
-  manifest.has_gpio_slot_been_defined == 'True'
   lsb.distributor_id == 'Ubuntu Core'
 category_id: com.canonical.certification::gpio
 plugin: resource