[DPG] duplicate generation of path_format_arguments in pageable prepare_request function

[kristapratico]

Not a huge deal, but we're generating duplicate code for the path_format_arguments under prepare_request:

swagger you can use to reproduce: https://github.com/kristapratico/azure-sdk-for-python/blob/regen-clu-archboard/sdk/cognitivelanguage/azure-ai-language-conversations/swagger/README.md

[iscai-msft]

fixed in #1307, should release that today. Closing 😏