[base] Remove GCC 4.8 Workaround in base::flat_tree

This change removes a GCC 4.8 work around the lack of
std::vector::erase(const_iterator) from base::flat_tree.

Bug: 682254, 677044
Change-Id: I8bd13851baa58c8cecd64c02c50bd999357afac4
Reviewed-on: https://chromium-review.googlesource.com/1005074
Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549809}
1 file changed