Adjust AppImage build of QtKeychain to be found by cmake

Now that things are done in a more standard way, let's adjust the
AppImage build so that QtKeychain is picked up properly now that our
FindQt5Keychain.cmake file is gone.

Signed-off-by: Kevin Ottens <kevin.ottens@nextcloud.com>

admin/linux/build-appimage.sh

@@ -30,7 +30,7 @@ mkdir build
 cd build
 cmake -D CMAKE_INSTALL_PREFIX=/usr ../
 make -j4
-make DESTDIR=/app install 
+make install
 
 #Build client
 cd /build
@@ -39,8 +39,6 @@ cd build-client
 cmake -D CMAKE_INSTALL_PREFIX=/usr \
     -D NO_SHIBBOLETH=1 \
     -D BUILD_UPDATER=ON \
-    -D QTKEYCHAIN_LIBRARY=/app/usr/lib/x86_64-linux-gnu/libqt5keychain.so \
-    -D QTKEYCHAIN_INCLUDE_DIR=/app/usr/include/qt5keychain/ \
     -DMIRALL_VERSION_SUFFIX=PR-$DRONE_PULL_REQUEST \
     -DMIRALL_VERSION_BUILD=$DRONE_BUILD_NUMBER \
     $DRONE_WORKSPACE