[Discuss] Remove adb-squid-proxy example

[r3stl355]

My reasoning:

• This is a standard workspace deployment from the Databricks point of view with an addition of a single notebook with short config is used to configure the cluster to use the proxy. Most of code is about deploying a squid VM which has nothing to do with Databricks
• Large monolithic deployment without significant reusable modules. There are some local modules but very use-case specific
• squid config notebook may no longer work with shared clusters, requires testing
• packer build . fails with failed to request token from metadata endpoint: Get "http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https%3A%2F%2Fmanagement.azure.com". (using az login authentication)
• there are no instructions for configuring packer and plugins, take a bit to figure that out

[alexott]

Most probably that's ok - @hwang-db wdyt?