Remove Qt6 apt packages - use aqt install-qt only

Removed 13 Qt6 packages from apt installation:
- libqt6core6, libqt6gui6, libqt6widgets6
- libqt6sql6, libqt6sql6-psql, libqt6test6
- qt6-base-dev, qt6-l10n-tools
- qt6-serialport-dev, qt6-svg-dev
- qt6-tools-dev-tools, qt6-tools-dev
- qt6-websockets-dev

Qt installation now uses ONLY aqt install-qt (lines 424-428)
System dependencies remain: build-essential, cmake, ninja-build, git, python3-pip, boost, kf6texttemplate, gtest/gmock, postgresql, vlc, ssl, xml, xerces

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

qt6-after/qt6-migrated-legatus/new_docker_build_release2.sh

@@ -411,19 +411,6 @@ apt-get install -y -qq \
   python3-pip \
   libboost-dev \
   libkf6texttemplate-dev \
-  libqt6core6 \
-  libqt6gui6 \
-  libqt6widgets6 \
-  libqt6sql6 \
-  libqt6sql6-psql \
-  libqt6test6 \
-  qt6-base-dev \
-  qt6-l10n-tools \
-  qt6-serialport-dev \
-  qt6-svg-dev \
-  qt6-tools-dev-tools \
-  qt6-tools-dev \
-  qt6-websockets-dev \
   libgtest-dev \
   libgmock-dev \
   libpq-dev \