Remove the provider_vtab

It's no longer needed with the newly added FuseDataProvider class. Also
cleans up the parameters for run_fuse_sideload.

Bug: 127071893
Test: unit tests pass, run a sideload
Change-Id: I1ccd6798d187cfc6ac9f559ffb3f3edf08dad55c
diff --git a/fuse_sideload/include/fuse_provider.h b/fuse_sideload/include/fuse_provider.h
index 672af05..499d57a 100644
--- a/fuse_sideload/include/fuse_provider.h
+++ b/fuse_sideload/include/fuse_provider.h
@@ -37,7 +37,7 @@
     return fuse_block_size_;
   }
 
-  explicit operator bool() const {
+  bool Valid() const {
     return fd_ != -1;
   }