streams: remove AutoFile::Get() entirely

Co-Authored-By: David Gumberg <davidzgumberg@gmail.com>

Github-Pull: bitcoin/bitcoin#30884
Rebased-From: a240e150e8

src/addrdb.cpp

@@ -73,7 +73,7 @@ bool SerializeFileDB(const std::string& prefix, const fs::path& path, const Data
         remove(pathTmp);
         return false;
     }
-    if (!FileCommit(fileout.Get())) {
+    if (!fileout.Commit()) {
         fileout.fclose();
         remove(pathTmp);
         LogError("%s: Failed to flush file %s\n", __func__, fs::PathToString(pathTmp));