Stop writing file paths into TIFF DocumentNames

File paths can contain confidential information such as usernames
and directory structures, making the previous behaviour a potential
privacy and security risk.

(cherry picked from commit a3a88bf6)
2 jobs for gimp-2-10 in 21 minutes (queued for 1 second)
Status Job ID Name Coverage
  Dependencies
passed #824516
deps-debian/testing

00:07:16

 
  Gimp
passed #824517
gimp-debian/testing-autotools

00:13:43