Revert "portalize drag urls"

This reverts commit 8d7e600f.

While this revert unfortunately removes Dolphin's ability to copy to
sandboxed applications, the bugs being temporarily fixed by this seem
more important. See the bugs mentioned below for details.

Especially copy-pasting needs to work flawlessly for an application
like Dolphin. After the revert this will either work correctly or – in
the case of sandboxed applications – not at all.

CCBUG: 457529
CCBUG: 462928