Fix malformed Android change markers.

These were not consistent with the style guide,
as enforced by the libcore-compare-upstreams tool.

Also improved the wording of a (previously malformed)
comment in InMemoryCookieStore.removeAll().

Test: Checked that the libcore-compare-upstreams
      tool no longer complains about malformed
      change markers after this CL.

Bug: 35910877
Change-Id: Ib83f819684ff309ea8e48d6767a84565739dff94