Don't try to use qtchooser

It actually appears to be deprecated and does not support Qt 6.

snap/snapcraft.yaml

@@ -49,7 +49,6 @@ parts:
       craftctl default
       craftctl set version="$(git describe | sed 's/v//')"
     override-build: |
-      qtchooser -list-versions
       qmake -version
       qmake -query
       qbs setup-toolchains --detect
@@ -58,8 +57,6 @@ parts:
     parse-info:
       - usr/share/metainfo/org.mapeditor.Tiled.appdata.xml
     source: .
-    build-environment:
-      - QT_SELECT: qt6
     build-packages:
       - build-essential
       - dpkg-dev
@@ -70,7 +67,6 @@ parts:
       - qt6-declarative-dev
       - qt6-l10n-tools
       - qt6-svg-dev
-      - qtchooser
       - zlib1g-dev
     # FIXME: Python plugin compiles and loads, but can't find platform libraries
     #  - python-dev