NIFI-8931 Remove OTP Authentication

[exceptionfactory]

Description of PR

NIFI-8931 Removes One-time Password authentication and associated token REST resources.

Transitioning to HTTP session cookies for passing JSON Web Tokens in #4988 eliminated the need for OTP authentication when downloading files or launching user interface extensions. Web browsers include HTTP session cookies on requests, which removes the requirement for JavaScript calls to request an access token prior to making requests.

Changes include removal of the OTP authentication services as well as the download-token and ui-extension-token REST Access Resources, along with the associated JavaScript code.

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[gresockj]

Verified that this still works with and without OIDC login. Tested downloading from the provenance screen and using a custom UI like JoltTransformJSON. Nice work cleaning up this portion of the code, @exceptionfactory!

[thenatog]

Tested this out with X509 and LDAP, was able to download flow file content, and view in the content browser. I was also able to download template files. Big chunk of code gone, awesome.
+1 wil merge.

[exceptionfactory]

Thanks for the review @thenatog!