Revert "feat(nginx): use slice module"

[ChandonPierre]

This reverts commit 9cd0135.

This seems to cause more problems than it solves -

< X-Docker-Registry-Proxy-Cache-Upstream-Status: HIT
< X-Docker-Registry-Proxy-Cache-Type: manifest-secondary
< Accept-Ranges: bytes
< 
* transfer closed with 1609 bytes remaining to read
* Closing connection 0
* TLSv1.3 (OUT), TLS alert, close notify (256):
curl: (18) transfer closed with 1609 bytes remaining to read

Since cache key is defined in common, slice module applies to manifests as well, which seems to lead to unexpected EOF pulling image manifests on occasion