CHE-4007: Remove deprecation in GitHubClientService

[vinokurig]

What does this PR do?

Remove deprecated methods in GitHubClientService class

What issues does this PR fix or reference?

fixes #4007

Changelog

Removed deprecated methods in GitHubClientService class

Release Notes

Technical debt N/A

Docs PR

Technical debt N/A

[codenvy-ci]

Build # 2775 - FAILED

Please check console output at https://ci.codenvycorp.com/job/che-pullrequests-build/2775/ to view the results.

[vinokurig]

[TEST]
[TEST] RESULTS ANALYSE:
[TEST]
[TEST] Command line: ./webdriver.sh --test=com.codenvy.ide.git.*
[TEST]
[TEST] Local results:
[TEST] 	- Run: 	     30
[TEST] 	- Failed:     3
[TEST]
[TEST] REGRESSION (3):
[TEST] 	com.codenvy.ide.git.ImportRecursiveSubmoduleTest.checkImportProjectSubmoduleByHttpsUrl
[TEST] 	com.codenvy.ide.git.ImportRecursiveSubmoduleTest.checkImportProjectSubmoduleBySshUrl
[TEST] 	com.codenvy.ide.git.ImportRecursiveSubmoduleTest.checkImportProjectSubmoduleFromGithub
[TEST]

[TEST] STABLE TESTS EXECUTION RESULTS ANALYSE:
[TEST]
[TEST] Command line: ./webdriver.sh --compare-with-ci
[TEST]
[TEST] CI results https://ci.codenvycorp.com/view/qa/job/che-integration-tests/363/
[TEST] 	- Failed:    81 (unique tests)
[TEST]
[TEST] Local results:
[TEST] 	- Run: 	      30
[TEST] 	- Failed:     3
[TEST] 	com.codenvy.ide.git.ImportRecursiveSubmoduleTest.checkImportProjectSubmoduleByHttpsUrl
[TEST] 	com.codenvy.ide.git.ImportRecursiveSubmoduleTest.checkImportProjectSubmoduleBySshUrl
[TEST] 	com.codenvy.ide.git.ImportRecursiveSubmoduleTest.checkImportProjectSubmoduleFromGithub
[TEST]
[TEST] Comparing with https://ci.codenvycorp.com/view/qa/job/che-integration-tests/363/
[TEST] If a test failed then it is NOT marked as regression.
[TEST]
[TEST] NO REGRESSION! CHECK THE FAILED TESTS. THEY MIGHT FAIL DUE TO DIFFERENT REASON.
[TEST]
[TEST]