Build: Fix static library building

Due to bugs in meson the approach with the intermediate static library for tests does not work very well, see #44 (closed). Therefore this commits removes that helper library and instead uses extract_all_objects for the tests.

Due to the removal of the static helper library, it means we can no longer force static linking for dav1d tool on windows which means that when building a shared library the dav1d.exe will not be runnable in the build directory again.

Fix #44 (closed)