Ash network icons: Remove unused label code and strings

In the new feature pod tray re-factoring, some strings and code that are
no longer in use got left behind, this cleans them up.

network_icon::GetLabelForNetwork was only getting called with icon_type
ICON_TYPE_MENU_LIST, and GetDefaultLabel was unused.

Bug: 862420
Change-Id: I538c9f65fe68df56c116a8be70c75cfb5c10f07c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614141
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661520}
9 files changed