[TASK] English XLIFF files should not contain target element

[TASK] English XLIFF files should not contain target element

Pootle uses the English XLIFF file has the template language and as such
it does not make sense to have "en" -> "en" translation files.

English XLIFF files are templates and should contain only a 'source', not
a 'target' element.

This commit contains:

- Remove of the target elements
- Remove target-language attribute
- Set the date attribute to the correct format
- Remove approved attribute

Change-Id: Ic118a746e93493f1a2b820f0e3721c53ca2d7805
Resolves: #31043
Relates: #30916
Releases: 4.6