[GTK] Fix linter warnings on the GTK Debug TestExpectation file and update some expec...

[GTK] Fix linter warnings on the GTK Debug TestExpectation file and update some expectations for Debug.

Unreviewed test gardening.

* TestExpectations: Merge expectations for imported/w3c/web-platform-tests/WebCryptoAPI/derive_bits_keys/pbkdf2.worker.html
* platform/gtk/TestExpectations: Mark observed timeouts on Debug and fix linter warnings related to tests renamed or deleted.
* platform/gtk/imported/w3c/web-platform-tests/fetch/api/basic/request-headers-expected.txt: Removed.
* platform/gtk/imported/w3c/web-platform-tests/fetch/api/basic/request-headers-worker-expected.txt: Removed.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@218230 268f45cc-cd09-0410-ab3c-d52691b4dbfc