[Release] remove usage of rgrep

doc/release/build.tex

@@ -7,10 +7,10 @@ The procedure for creating the source distribution.
 \begin{itemize}
 \item All tools needed to compile Frama-C (that you should have anyways)
 \item \texttt{bash} v4.0 or higher
-\item \texttt{rgrep}
 \item \texttt{git-lfs}
 \item GNU \texttt{parallel}
 \item a \TeX distribution
+\item \texttt{latexmk}
 \item (recommended) \texttt{texfot}
 \end{itemize}
 

doc/release/checktar.sh

@@ -32,7 +32,7 @@ do
     fi
 done
 
-RESULT=$(rgrep $HOME $DIR)
+RESULT=$(grep -Iir $HOME $DIR)
 
 if [[ "$RESULT" != "" ]]; then
     echo "### ERROR: Found some $HOME occurrences in the distribution"