ui-tree: Remove unnecessary path breadcrumb navigation

The path breadcrumb navigation at the top of the 'tree' page has now been
duplicated in ui-shared, which leaves the ui-tree implementation unnecessary.

This patch removes the breadcrumb navigation from ui-tree, and moves the
"(plain)" link that followed the breadcrumb when displaying blobs to the
end of the next line, following the blob SHA1.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>