use boost 1.73.0

appveyor.yml

@@ -21,11 +21,8 @@ install:
   - cmd: chdir %ICUWIN%
   - cmd: curl -L -o icu.zip https://github.com/unicode-org/icu/releases/download/release-65-1/icu4c-65_1-Win64-MSVC2017.zip
   - cmd: 7z x icu.zip
-  # Install boost
-  - cmd: chdir %APPVEYOR_BUILD_FOLDER%
-  - cmd: vcpkg install boost
-  - cmd: set BOOST_ROOT=%VCPKG_ROOT%\installed\x86-windows
   # Set up the build environment
+  - cmd: set BOOST_ROOT=C:\Libraries\boost_1_73_0
   - cmd: '"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" x86_amd64'
   # build wxWidgets
   - cmd: chdir %WXWIN%\build\msw