Issue #3 -- Drop SHF_WRITE flag from .plt attributes

The table titled "special sections" displays the SHF_WRITE flag as being
set in the ".plt" section's attributes.  This looks like a documentation
bug that has been present since the original ABI.  The .plt doesn't need
to be writable, and it would pose a security risk if it were.

To my knowledge (verified with Ulrich Weigand and Andreas Krebbel),
existing tools never mark the .plt writable.

To fix the issue, just drop the SHF_WRITE flag from the ".plt" section's
attributes.

lzsabi.tex

@@ -4048,7 +4048,7 @@ \subsection{Special Sections}
     \texttt{.got} & \texttt{SHT\_PROGBITS} &
     \texttt{SHF\_ALLOC + SHF\_WRITE} \\
     \texttt{.plt} & \texttt{SHT\_PROGBITS} &
-    \texttt{SHF\_ALLOC + SHF\_WRITE + SHF\_EXECINSTR} \\
+    \texttt{SHF\_ALLOC + SHF\_EXECINSTR} \\
     \bottomrule
   \end{tabular}
   \end{DIFnomarkup}