Remove DDR_INNER_LOOP

Remove DDR_INNER_LOOP

...since it was only ever zero in practice.  I wondered about making
it a symbolic constant instead, but it didn't seem worth it when
there was only one user (and that user was part of the internal
tree-data-ref.c implementation).

2019-04-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-data-ref.h (data_dependence_relation::inner_loop): Delete.
	(DDR_INNER_LOOP): Likewise.
	* tree-data-ref.c (dump_data_dependence_relation): Update accordingly.
	(initialize_data_dependence_relation): Likewise.
	(insert_innermost_unit_dist_vector): Use 0 instead of DDR_INNER_LOOP.

From-SVN: r270654