configure.ac: remove stale LT_INIT options

1. We haven't used the -dlopen or -preopen options for years (if
   ever?); no need for the `dlopen` LT_INIT option.
2. We haven't supported Windows for years; no need for the `win32-dll`
   LT_INIT option.

Also, this commit includes a minor fix to a comment.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

configure.ac

@@ -1207,7 +1207,7 @@ fi
 # if we have a C++ compiler.
 AS_IF([test "$OMPI_TRY_FORTRAN_BINDINGS" = "$OMPI_FORTRAN_NO_BINDINGS"],[F77=no FC=no])
 
-LT_INIT([dlopen win32-dll])
+LT_INIT
 
 # What's the suffix of shared libraries?  Inspired by generated
 # Libtool code (even though we don't support several of these
@@ -1243,7 +1243,7 @@ esac
 AC_SUBST(OPAL_DYN_LIB_PREFIX)
 AC_SUBST(OPAL_DYN_LIB_SUFFIX)
 
-# Need the libtool binary before the rpathify stuff
+# Need the libtool executable before the rpathify stuff
 LT_OUTPUT
 
 ##################################