NO_KERNEL_SOURCES left behind

This looks like a leftover from a141d71531.

All occurrences of NO_KERNEL_SOURCES should have been replaced by
the negated KERNEL_SOURCES.

Though probably isTrue should be used for all boolean options, to avoid
confusion when setting them in the config file (some of them should be
set to 0 or 1, while others support yes/no/0/1/true/false).

gen_package.sh

@@ -155,7 +155,7 @@ gen_kerncache_extract_config()
 gen_kerncache_is_valid()
 {
     KERNCACHE_IS_VALID=0
-    if [ "${NO_KERNEL_SOURCES}" = '1' ]
+    if [ "${KERNEL_SOURCES}" = '0' ]
     then
 
         BUILD_KERNEL=0