file_test: Fix file test

Trimming of the line feed is no longer necessary after
https://github.com/file/file/commit/d993c6b0db20711b2c4cb9d2bee8c7f2e59b0a43

Currently the tests:

• bcachefs2
• gpkg-1-zst
• multiple

are failing, but a fix will be committed upstream.

This also reverts c5e957ad4 "file: fix test case for gpkg by removing the extra \n."

MFC after: 3 days