Drop .Extensions from Steeltoe.Logging namespace

[bart-vmware]

Description

Similarly to what we did for Steeltoe.Configuration in #1008, this PR drops ".Extensions" from the Steeltoe.Logging namespace.

Quality checklist

• Your code complies with our Coding Style.
• You've updated unit and/or integration tests for your change, where applicable.
• You've updated documentation for your change, where applicable.
  If your change affects other repositories, such as Documentation, Samples and/or MainSite, add linked PRs here.
• There's an open issue for the PR that you are making. If you'd like to propose a new feature or change, please open an issue to discuss the change or find an existing issue.
• You've added required license files and/or file headers (explaining where the code came from with proper attribution), where code is copied from StackOverflow, a blog, or OSS.

[dtillman]

LGTM