Delete old logo file

[asarraf]

dbt-logo.png is the old logo and hence can be deleted.

resolves dbt-labs#890

Problem

In the dbt-utils repo we are still preserving the old logo.
We no longer use this logo; the new logo has been replaced everywhere.
This PR works on the decommissioning of the old logo completely from the Repo

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Solution

We are deleting the etc Directory from the Repo -> https://github.com/dbt-labs/dbt-utils

Checklist

• This code is associated with an issue which has been triaged and accepted for development.
• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the README.md (if applicable)