Revert "Allow to set display "inline" on legend element"

This reverts commit 2383abb8b227d12ae53f2b163b57e02ff63dbf0b.

Reason: it violates the spec that says that fieldset's legend should be
displayed as a block box (overriding any explicit 'display' value).
Also it introduces an interop issue with Firefox
https://bugzilla.mozilla.org/show_bug.cgi?id=653870.

BUG=481983

Review-Url: https://codereview.chromium.org/2447843002
Cr-Commit-Position: refs/heads/master@{#427364}
5 files changed