AgentServer: remove unnecessary QWidgets import

2 jobs for !60 with no-qwidget-agentserver in 15 minutes and 58 seconds (queued for 10 minutes and 50 seconds)
latest detached
Status Job ID Name Coverage
  Build
failed #104146
build_clazy_clang_tidy

00:04:49

passed #104145
linux kf5-qt5 qt5.15

00:11:09

1.0%
 
Name Stage Failure
failed
build_clazy_clang_tidy Build
[ 24%] Linking CXX static library ../../lib/libakonadiserver.a
[ 24%] Built target libakonadiserver
make: *** [Makefile:160: all] Error 2
Uploading artifacts for failed job
Uploading artifacts...
WARNING: build/clang-tidy-report.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 1