drm/i915: Drop debugfs/i915_next_seqno

Having just gutted the implementation as there is no global seqno
tracking, remove the vestigal write-only stub for debugfs/i915_next_seqno.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181228140736.32606-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1038,16 +1038,6 @@ static const struct file_operations i915_error_state_fops = {
 };
 #endif
 
-static int
-i915_next_seqno_set(void *data, u64 val)
-{
-	return val ? 0 : -EINVAL;
-}
-
-DEFINE_SIMPLE_ATTRIBUTE(i915_next_seqno_fops,
-			NULL, i915_next_seqno_set,
-			"0x%llx\n");
-
 static int i915_frequency_info(struct seq_file *m, void *unused)
 {
 	struct drm_i915_private *dev_priv = node_to_i915(m->private);
@@ -4811,7 +4801,6 @@ static const struct i915_debugfs_files {
 	{"i915_gpu_info", &i915_gpu_info_fops},
 #endif
 	{"i915_fifo_underrun_reset", &i915_fifo_underrun_reset_ops},
-	{"i915_next_seqno", &i915_next_seqno_fops},
 	{"i915_pri_wm_latency", &i915_pri_wm_latency_fops},
 	{"i915_spr_wm_latency", &i915_spr_wm_latency_fops},
 	{"i915_cur_wm_latency", &i915_cur_wm_latency_fops},