Documentation: remove a redundant elaboration

Documentation: remove a redundant elaboration

The comment in parentheses is wrong, as one has to leave out both the
colon and <dst>. This situation is covered by the section a few lines
down:

  A parameter <ref> without a colon pushes the <ref> from the source
  repository to the destination repository under the same name.

So, just remove the parentheses.

Signed-off-by: Anders Melchiorsen <redacted>
Signed-off-by: Junio C Hamano <redacted>