Remove the squid plugin from 1.4-dev

Description

Remove the squid plugin from 1.4-dev

Plugin with the defect

squid

Additional Information

date back to gosa2 days, no supported by squid itself, dead code

changed milestone to %FusionDirectory 1.4

added PJ1802-0188 label

mentioned in commit 74976d4a

added Removed label

added 20m of time spent at 2021-01-28

added release notes label