How to delete all files in a folder inside an archive with 7zip?

Question

I have an archive file, which has a lot of folders inside of it:

- myfile.zip
  - folder1
  - folder2
  - folder3
     - folder3file1.txt
     - folder3file2.txt

How can I delete all files from the folder3, without deleting that folder, in one command line?

I know only the way to delete the folder3, and then add it as a new, empty folder, but this causes double 7zip information printing to command line.

Or how could I set to not to print the 7zip informations during 7z commands?