image.bbclass: delete DATE variable too

When creating a custom image which uses the DATE variable the basehash
seems to change every day and lead to errors such as:
ERROR: console-tdx-image-2.7.6-r0 do_image_customimg: Error executing a python function in exec_python_func() autogenerated:

The stack trace of python calls that resulted in this exception/failure was:
File: 'exec_python_func() autogenerated', lineno: 2, function: <module>
     0001:
 *** 0002:set_image_size(d)
...

Add DATE to the variables which should not get expanded early and to the
vardepsexclude list for the image task.

(From OE-Core rev: 4af13a4855c74cea9cf6c168fd73165d7094bf93)

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/image.bbclass

@@ -437,6 +437,7 @@ python () {
         # date/time values. It will get expanded at execution time.
         # Similarly TMPDIR since otherwise we see QA stamp comparision problems
         localdata.delVar('DATETIME')
+        localdata.delVar('DATE')
         localdata.delVar('TMPDIR')
 
         image_cmd = localdata.getVar("IMAGE_CMD")
@@ -501,7 +502,7 @@ python () {
         d.prependVarFlag(task, 'postfuncs', ' create_symlinks')
         d.appendVarFlag(task, 'subimages', ' ' + ' '.join(subimages))
         d.appendVarFlag(task, 'vardeps', ' ' + ' '.join(vardeps))
-        d.appendVarFlag(task, 'vardepsexclude', 'DATETIME')
+        d.appendVarFlag(task, 'vardepsexclude', 'DATETIME DATE')
 
         bb.debug(2, "Adding task %s before %s, after %s" % (task, 'do_image_complete', after))
         bb.build.addtask(task, 'do_image_complete', after, d)