chore: drop Qt 5 support

The required exiv2 version is now 0.28.x as well since it was
keeped for Qt 5 build.

Due to exiv2ConfigVersion.cmake doesn't allow us write something
like find_package(exiv2 "0.28") to require version >= 0.28.0,
we simply don't put the required version number here for now.

appveyor.yml

@@ -12,18 +12,10 @@ environment:
       QTDIR: C:\Qt\6.8\mingw_64
       MINGW64: C:\Qt\Tools\mingw1310_64
       KF_BRANCH: master
-      EXIV2_VERSION: "0.28.3"
+      EXIV2_VERSION: "0.28.5"
       EXIV2_CMAKE_OPTIONS: "-DEXIV2_ENABLE_BROTLI=OFF -DEXIV2_ENABLE_INIH=OFF -DEXIV2_BUILD_EXIV2_COMMAND=OFF"
       PPIC_CMAKE_OPTIONS: "-DPREFER_QT_5=OFF"
       WINDEPLOYQT_ARGS: "--verbose=2 --no-quick-import --no-translations --no-opengl-sw --no-system-d3d-compiler --skip-plugin-types tls,networkinformation"
-    - job_name: mingw81_64_qt5_15_2
-      QTDIR: C:\Qt\5.15.2\mingw81_64
-      MINGW64: C:\Qt\Tools\mingw810_64
-      KF_BRANCH: kf5
-      EXIV2_VERSION: "0.27.7"
-      EXIV2_CMAKE_OPTIONS: "-DEXIV2_BUILD_SAMPLES=OFF -DEXIV2_ENABLE_WIN_UNICODE=ON -DEXIV2_BUILD_EXIV2_COMMAND=OFF"
-      PPIC_CMAKE_OPTIONS: "-DPREFER_QT_5=ON"
-      WINDEPLOYQT_ARGS: "--verbose=2 --no-quick-import --no-translations --no-opengl-sw --no-angle --no-system-d3d-compiler"
 
 install:
   - mkdir %CMAKE_INSTALL_PREFIX%