(bug 59636) should not override global h1 and h2 style

* Removed h1 override - the new typography refresh h1 style is fine
* More specific h2-score, to override typography refresh
  * Added font-family: sans-serif
* Removed line between "Appears on <page>" & the history entries, because
  h1 now already has a line + board history has no "Appears on <page>"
  text. If we still want a deviding line, it probably needs to look
  differently, and be on .flow-history-pages instead of .flow-history-log
  (so it doesn't appear on board history)

Bug: 59636
Change-Id: I5c8c741c4e05359b66164519dc02ba567b4349ca
Merge "(bug 59636) should not override global h1 and h2 style"