Remove unnecessary wxCONFIGURE_FLAGS environment variable

It was confusing to have both it and wxCONFIGURE_OPTIONS, so remove it
and just use its value as part of wxCONFIGURE_OPTIONS.

No real changes.

.github/workflows/ci_mac.yml

@@ -99,7 +99,6 @@ jobs:
           allow_warnings: true
 
     env:
-      wxCONFIGURE_FLAGS: --disable-sys-libs --without-liblzma ${{ matrix.configure_flags }} --prefix=${{ github.workspace }}/localbin_${{ matrix.arch }}
       wxUSE_ASAN: ${{ matrix.use_asan && 1 || 0 }}
       DEVELOPER_DIR: /Applications/Xcode.app/Contents/Developer
       NSUnbufferedIO: YES
@@ -160,7 +159,7 @@ jobs:
 
     - name: Configuring
       run: |
-        wxCONFIGURE_OPTIONS="--disable-optimise $wxCONFIGURE_FLAGS"
+        wxCONFIGURE_OPTIONS="--disable-optimise --disable-sys-libs --without-liblzma ${{ matrix.configure_flags }} --prefix=${{ github.workspace }}/localbin_${{ matrix.arch }}"
 
         if [ -n "${{ matrix.xcode_sdk }}" ]; then
           sdk_path=`xcrun --sdk ${{ matrix.xcode_sdk }} --show-sdk-path`