Bug#1093229: plakativ: FTBFS with fitz_old import

[Bastian Germann]

Source: plakativ
Severity: serious
Version: 0.5.2-2

This is a follow-up on #1071861.
plakativ fails to build from source because python3-fitz has moved to the 
current build with the import name fitz (or pymupdf).
The #1071861 changes need to be reverted to deal with this.