Remove documentation of removed option

doc/doxygen/chapters/41configure_options.doxy

@@ -465,14 +465,6 @@ Enable the compilation and the execution of the libstarpufft examples.
 By default, they are neither compiled nor checked.
 </dd>
 
-<dt>--with-magma=<c>prefix</c></dt>
-<dd>
-\anchor with-magma
-\addindex __configure__--with-magma
-Search for MAGMA under <c>prefix</c>.  <c>prefix</c> should notably
-contain <c>include/magmablas.h</c>.
-</dd>
-
 <dt>--with-fxt=<c>prefix</c></dt>
 <dd>
 \anchor with-fxt