Currently qtloader.js fetches and copies the files manually. By doing
so we are missing some preproccessing by Emscripten preload plugins.
Use Emscripten API to preload files, so preload plugin for .so can
download, compile and resolve dependencies of imported shared libraries.
This makes looking for dependencies in preload_qml_import.py no longer
needed. Remove redundant code.
Fixes: QTBUG-121817
Change-Id: Idd35f25d5f54123910f813a636407eea23e157cb
Reviewed-by: Piotr Wierciński <piotr.wiercinski@qt.io>
a6e7274704