Turn off dev_installer_prebuilts in firmware builders.
Turn off dev_installer_prebuilts in firmware builders.

Fixes the following error:
http://chromegw/i/chromiumos.tryserver/builders/link-depthcharge-firmware/builds/1

BUG=chrome-os-partner:17147
TEST=Trybot run.

Change-Id: I3070602dc6d7e7576a97737d6ecdd6a467986d03
Reviewed-on: https://gerrit.chromium.org/gerrit/41127
Reviewed-by: Chris Sosa <959d3d631fb6f17f1b07f751372041a1edb210d1@chromium.org>
Commit-Queue: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: Gabe Black <5c8aa1266c03186393d9e7b3b4e3b14239af8201@chromium.org>

coreos/chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,coreos/chromite,chadversary/chromiumos.chromite,zhang0137/chromite,zhang0137/chromite,zhang0137/chromite,coreos/chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite