This moves dim and dimen fields from gfc_array_info to gfc_ss.
The gfc_ss::data::temp::dimen field is also removed as it is now redundant.
The only non-trivial change is the removal of the dim array initialization in
gfc_conv_loop_setup (when the temp_ss's type is changed from GFC_SS_TEMP
to GFC_SS_SECTION) made useless by the apperance of the very same initialization
earlier in gfc_get_temp_ss.
OK?