mirror: "all": spurious ticks

[thchr]

The documentation of mirror states that:

If "all", axis lines are mirrored on all shared-axes subplots. If "allticks", axis lines and ticks are mirrored on all shared-axes subplots.

I.e., from what I gather mirror: "all" should not put any tick marks but merely draw a line. Presently, however, it does put tick marks on the mirrored axis of the first subplot (or even solitary plot).

Previously, a variant of this was noted in #4136 where mirror: "all" would behave like mirror: "allticks". This was addressed in #4140, but the fix seems only to have addressed part of the issue, however. Specifically:

	Example	Behavior
Before #4140 (v1.49.3)	https://codepen.io/thchr/pen/yLbpowE	Ticks on all mirrored axes
After #4140 (v1.49.4 and later)	https://codepen.io/thchr/pen/qBmpXge	Ticks on mirrored axis of first subplot

What I thought expected behavior would be is this (i.e. tick on no mirrored axis; only the left-most non-mirrored y-axis of the first subplot):