Boot time labs: fix path and simplify explanations

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

labs/boot-time-application/boot-time-application.tex

@@ -50,7 +50,7 @@ \subsection{Compiling ffmpeg with a reduced configuration}
 options are:
 
 \begin{verbatim}
-cd ~/boot-time-labs/rootfs/buildroot-arm/output/build/ffmpeg-4.2.4
+cd ~/boot-time-labs/rootfs/buildroot/output/build/ffmpeg-4.3.2
 ./configure --help
 \end{verbatim}
 
@@ -64,10 +64,6 @@ \subsection{Compiling ffmpeg with a reduced configuration}
 Following these findings, here's how we are going to modify Buildroot's
 configuration for \code{ffmpeg}.
 
-This time, let's assume that the {\em Thumb2} build from the previous
-lab has completed. If that's the case, finish that lab (measuring and
-writing down size and performance), and come back here when you are done:
-
 \begin{verbatim}
 cd ~/boot-time-labs/rootfs/buildroot/
 make menuconfig
@@ -269,9 +265,7 @@ \section{Putting things back together}
 
 Update and reboot your system through \code{grabserial}, and copy and
 paste your output to \code{boot-time-labs/logs/application.log}.
-Fill the below table with updated figures (we don't expect earlier
-parts of system bootup to be impacted... scripts may run faster after
-being recompiled in \code{Thumb2}):
+Fill the below table with updated figures:
 
 \begin{tabular}{| l | l | r |}
   \hline