Revert "metadata: add support for fields that are not empty but have omitempty"

This reverts commit 3a089165333d948292c4bcb6ba95318716b72edc.
Revert "metadata: fix formatting"

This reverts commit beef15af4ec734a3954d3959b069e0bd2b4f6fb0.
Revert "metadata: add support for struct tag options"

This reverts commit cdda3797418451848f3bc612187abee83341fe42.