Remove vendored usvfs and Windows-only usvfs code paths

The Linux port uses its own in-process FUSE VFS (FuseConnector), so
usvfs was dead weight: libs/usvfs/ was never built, usvfsconnector.cpp
was explicitly REMOVE_ITEM'd from the source list, and every call site
was already guarded by #ifdef _WIN32 with a working Linux branch (the
Windows build is also broken on this branch, since FUSE3 is a hard
find_package dependency).

- Drop libs/usvfs/ and src/src/usvfsconnector.{cpp,h}
- Collapse #ifdef _WIN32 / usvfs include branches in organizercore,
  mainwindow, settings, util, spawn
- Remove getUsvfsVersionString() and the "usvfs: ..." log field
- Remove vfs32/64DLLName APPPARAMs (nothing reads them)
- Relabel About dialog "usvfs:" row to "VFS: FUSE 3"

0 files changed, 0 insertions, 0 deletions