The DLL ships with the games and having the built-in version in
system32/syswow64 has unexpected consequences.
If the game is launched from a subdirectory, but the DLL is in current
working directory, the built-in takes precedence as CWD has lower search
priority than system directories (with the default SafeDllSearchMode).
By not installing amd_ags_x64.dll in system32/syswow64 the built-in is
still picked up correctly from lib/ when necessary.
There's an accompanying patch for wine that makes sure wineboot won't
install the dll, but since we construct our default_pfx in a special way
we also need to make sure that files won't get copied/linked there.
To make prefix updates smooth this change also removes any stale
amd_ags_x64.dlls that may have been installed by previous version of
Proton.
CW-Bug-Id: 18804
