[REMOVAL] remove unused ci bash scripts

[dbarker]

#3486 changed third party package build and install to use a single CMake project and the ExternalProject module. The old ci bash scripts for installing abseil, protobuf, and googletest can be removed.

Changes

• removes install_abseil.sh, install_protobuf.sh, and setup_googletest.sh

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

Name	Link
🔨 Latest commit	a1280e3
🔍 Latest deploy log	https://app.netlify.com/projects/opentelemetry-cpp-api-docs/deploys/6876923b3517cb0008147888

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.98%. Comparing base (4da9b67) to head (a1280e3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3541   +/-   ##
=======================================
  Coverage   89.98%   89.98%           
=======================================
  Files         219      219           
  Lines        7044     7044           
=======================================
  Hits         6338     6338           
  Misses        706      706           

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[lalitb]

LGTM