dropuser: add page

[almightyDavid]

• The page(s) are in the correct platform directories: common, linux, osx, windows, sunos, android, etc.
• The page(s) have at most 8 examples.
• The page description(s) have links to documentation or a homepage.
• The page(s) follow the content guidelines.
• The page(s) follow the style guide.
• The PR title conforms to the recommended templates.
• Version of the command being documented (if known): 17

[tldr-bot]

The build for this PR failed with the following error(s) at commit
9f8267deb5d37eb5900558fe0ae8aec91b042413:

pages/common/dropuser.md:25: TLDR008 File should contain no trailing whitespace

Please fix the error(s) and push again.