Bug 1077214 - Don't export DLLFLAGS from main configure. r=mshal

DLLFLAGS was exported from main configure so that it would be picked by NSPR
configure, allowing to pass down flags to link NSPR against mozglue. With
MOZ_FOLD_LIBS always enabled on MSVC builds, that is not necessary anymore
since the NSPR build system doesn't build any shared library anymore.

configure.in

@@ -7173,8 +7173,6 @@ else
       DLLFLAGS="$DLLFLAGS -LIBPATH:\$(DIST)/lib -DEFAULTLIB:mozglue"
     fi
     rm crtdll.obj
-
-    export DLLFLAGS
     ;;
   *)
     AC_MSG_ERROR([--enable-jemalloc not supported on ${target}])