Remove prebuilts that don't exist.

Remove prebuilts that don't exist.

x86-dogfood doesn't have automatically updated prebuilts anymore, so we should remove the broken binhost.

x86-alex should have automatically updated prebuilts, but
this particular one is out of date. So let's delete the
broken one and wait for the bots to put in a working one.

Here's the warning Greg Spencer got:

Fetching bininfo from http://chromeos-prebuilt/board/x86-alex/master-19.01.11.152857/packages/
!!! Error connecting to 'http://chromeos-prebuilt/board/x86-alex/master-19.01.11.152857/packages/'.
!!! Unable to get listing: 404 Server did not respond successfully (404: Not Found)

BUG=chromium-os:12527
TEST=emerge-x86-alexa -gp chromeos and verify warning is gone

Change-Id: I045bccd5db291228eaf85faa35dc7098514dafd7

[scottz-goog, 2011-02-25 18:40:54]

http://codereview.chromium.org/6591003/diff/1/overlay-x86-alex/prebuilt.conf
File overlay-x86-alex/prebuilt.conf (left):

http://codereview.chromium.org/6591003/diff/1/overlay-x86-alex/prebuilt.conf#...
overlay-x86-alex/prebuilt.conf:1:
PORTAGE_BINHOST="http://chromeos-prebuilt/board/x86-alex/master-19.01.11.152857/packages/"
Why don't we just update this to the latest:
http://chromeos-prebuilt.corp.google.com/board/x86-alex/master-24.02.11.07382...

those are actually there, ill track down why it isn't properly being updated.