Remove incorrect readme

[tim-pugh]

Remove incorrect readme that references a different AWS Lambda function

Issue #, if available:

Description of changes:
Removes the readme which talks about a Lambda slack function
Description of how you validated changes:
I took a look at the code
Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #1121 into develop will increase coverage by 0.1%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop    #1121     +/-   ##
==========================================
+ Coverage    94.76%   94.87%   +0.1%     
==========================================
  Files           71       69      -2     
  Lines         3476     3334    -142     
  Branches       678      651     -27     
==========================================
- Hits          3294     3163    -131     
+ Misses          93       89      -4     
+ Partials        89       82      -7

Impacted Files	Coverage Δ
samtranslator/model/eventsources/push.py	88.6% <0%> (-0.45%)	⬇️
samtranslator/swagger/swagger.py	95.68% <0%> (-0.26%)	⬇️
...lator/plugins/application/serverless_app_plugin.py	83.44% <0%> (-0.11%)	⬇️
samtranslator/plugins/globals/globals.py	99% <0%> (-0.03%)	⬇️
samtranslator/translator/verify_logical_id.py	100% <0%> (ø)	⬆️
samtranslator/translator/translator.py	99% <0%> (ø)	⬆️
samtranslator/plugins/__init__.py	100% <0%> (ø)	⬆️
samtranslator/model/sqs.py
samtranslator/model/cognito.py
samtranslator/model/api/api_generator.py	96.67% <0%> (+0.02%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fd718bb...aed4fb2. Read the comment docs.

[praneetap]

Thanks for catching these!