[HttpFoundation] Fixed removing a nonexisting namespaced attribute.
merged branch jakzal/bugfix/remove-nonexisting-attr-8387 (PR #8790)

This PR was merged into the 2.2 branch.

Discussion
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[HttpFoundation] Fixed removing a nonexisting namespaced attribute

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8387
| License       | MIT
| Doc PR        | -

Commits
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85a9c9d [HttpFoundation] Fixed removing a nonexisting namespaced attribute.