Remove redundant comments in credentials_factory.py

This is a follow-up patch for [1] to fix some nits. It is to remove
redundant comments for get_credentials function, as the comments have
already been included in docstring.

[1] Idd258f00999248a5422876d2d943f1e0595f4a69

Change-Id: I9b17100a86fc24dd575e50f3fcf29ae38ff4d3ec
diff --git a/tempest/common/credentials_factory.py b/tempest/common/credentials_factory.py
index 5dc1a3e..cecb8e3 100644
--- a/tempest/common/credentials_factory.py
+++ b/tempest/common/credentials_factory.py
@@ -265,8 +265,6 @@
     return credentials
 
 
-# Wrapper around auth.get_credentials to use the configured identity version
-# if none is specified
 def get_credentials(fill_in=True, identity_version=None, **kwargs):
     """Get credentials from dict based on config