Fix some non-fatal WebKitLegacy linker warnings about WebPreferences categories
Pull request: https://github.com/WebKit/WebKit/pull/6179
Committed 256369@main (4c7eca9bea82): <https://commits.webkit.org/256369@main> Reviewed commits have been landed. Closing PR #6179 and removing active labels.
<rdar://problem/102002855>