cmd/upspinserver: remove redundant imports
cmd/upspinserver: remove redundant imports

These packers are already _ imported in main.go.

Change-Id: I18d43a7f4d7e1ba957bdefcc9540bdd4a0a2b72c
Reviewed-on: https://upspin-review.googlesource.com/7870
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@google.com>
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin