[infra] Remove bullseye-updates from dockerfile

This made the docker build work for me locally. The "updates" list was
probably needed on jessie but isn't needed on bullseye anymore.

Change-Id: I88f257b928f6ef690dac9e7d450eaa4c2ea12b2f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/271102
Reviewed-by: William Hesse <whesse@google.com>

Author: athomas

tools/linux_dist_support/Debian.dockerfile

@@ -3,7 +3,6 @@
 # BSD-style license that can be found in the LICENSE file.
 FROM launcher.gcr.io/google/debian11:latest
 ARG depot_tools
-RUN sed -i /bullseye-updates/d /etc/apt/sources.list
 RUN apt-get update \
   && apt-get install -y build-essential debhelper git python3 \
   && rm -rf /var/lib/apt/lists/*