Remove cargo linker config for rust app

Removes cargo config to improve compatibility for apps that may be built without Clickable. The linker is instead configured via an env var in the docker image.

Before merging this:

• Merge clickable-docker-images!88 (merged)
• Merge clickable-docker-images!90 (merged)
• Merge and release clickable!479 (merged)
• Merge and release clickable!486 (merged)
• Set clickable_minimum_required to the new Clickable version

Contributes to clickable#332 (closed)