Revert "adbd: don't close ep0 until we receive FUNCTIONFS_UNBIND."

We're only reading FUNCTIONFS_BIND on creation upon the first creation
of the control fd, which results in an abort when rebind happens (e.g.
when MTP is enabled) and we unexpectedly read FUNCTIONFS_BIND in the
second instantiation of the connection.

This reverts commit 2b668d39.

Bug: http://b/135155652
Test: manually enabled MTP