Visual Studio project: build caching is broken

[gdevillele]

Compilation caching has been broken by the addition of libpng in the deptool process.
If you remove the deptool autoconfig call, it fixes it.

Notes

• project still compiles libpng source code, we still need to switch to precompiled libraries (I don't know about the difficulty)
• switching to precompiled libraries might just fix the issue (as libluau was not causing issues AFAIK)
• avoid to copy the _active_ directory when not needed might be a fix as well