Blender Git Loki

Fix T89592: Can't remove keyframes without active keying set

Partially revert 7fc220517f87a2c40a4f438a50485233ae6ed62f, as it
introduced two issues:

- Deleting keys without active keying set was no longer possible, and
- there was no more confirmation popup.

Pressing {key Alt I} in the 3D Viewport now executes
`ANIM_OT_keyframe_delete_v3d`, adjusted to suit both T88068 and T89592:

- If there is an active keying set, delete keys according to that keying
set.
- Otherwise, behave as `ANIM_OT_keyframe_delete_v3d` did before, that
is, delete all keyframes of the selected object and in pose-mode also
of selected bones.