Revert "Use ostringstream instead of printf formatting"

This reverts commit 2755de2.
Clang does not want to compile the code because the char array
passed to Error is not a literal string.

IOPool/TFileAdaptor/src/TStorageFactoryFile.cc

@@ -17,7 +17,6 @@
 #include <fcntl.h>
 #include <iostream>
 #include <cassert>
-#include <sstream>
 
 #if 0
 #include "TTreeCache.h"
@@ -415,9 +414,7 @@ TStorageFactoryFile::ReadBuffersSync(char *buf, Long64_t *pos, Int_t *len, Int_t
     std::vector<IOPosBuffer> &iov = repacker.iov();
     IOSize result = storage_->readv(&iov[0], iov.size());
     if (result != io_buffer_used) {
-      std::ostringstream ostr;
-      ostr<<"Storage::readv returned different size result="<<result<<" expected="<<io_buffer_used;
-      Error("ReadBuffersSync",ostr.str().c_str());
+      Error("ReadBuffersSync","Storage::readv returned different size result=%ld expected=%ld",result,io_buffer_used);
       return kTRUE;
     }
     xstats.tick(io_buffer_used);