Remove shared image information once it's been inserted in the Post

[mzorz]

Fixes #9408

This PR removes Intent.EXTRA_STREAM extra from the intent once it's been processed, to avoid re-inserting same media on each Activity re-creation.

Similar to what we did back in 277b69a in PR #6786

To test:

1. open the Photos app
2. pick an image
3. share to WP
4. select a site on the WP app and choose "create new post"
5. once the editor opens and the image starts uploading, rotate the device
6. verify it's still one image being uploaded, and no duplicates appear.

Update release notes:

• If there are user facing changes, I have added an item to RELEASE-NOTES.txt.

[mzorz]

cc @jtreanor for the cut to beta

[daniloercoli]

I've found a case where the shared picture is re-added multiple times.

To test:
0. Enable don't keep activities

1. open the Photos app
2. pick an image
3. share to WP
4. select a site on the WP app and choose "create new post"
5. once the editor opens and the image starts uploading (you can even let it uploading and finish) Tap the home button
6. Wait a bit and tap on the WP icon
7. Boom, the editor is reload and the picture added again.

[mzorz]

Nice find there @daniloercoli ! Made a small adjustment in 6bceb03 to not allow this 👍

[daniloercoli]

LGTM!