Boot time slides: don't suggest that ext4 is the best FS

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>

slides/boot-time-filesystems/boot-time-filesystems.tex

@@ -49,8 +49,7 @@ \section{Filesystem optimizations}
 \frametitle{Block filesystems}
 For block storage
 \begin{itemize}
-\item ext4: best for rather big partitions, good read and write
-      performance.
+\item ext4: pretty good read and write performance.
 \item xfs, jfs, reiserfs: can be good in some read or write scenarii
       as well.
 \item btrfs, f2fs: can achieve best read and write performance,