This reverts commit 6ab17a84 since it,
according to Benjamin, causes issues with slot assignment:

E: 15.669119 0000 0000 0000     # ------------ SYN_REPORT (0) ----------
E: 15.954242 0003 002f 0000     # EV_ABS / ABS_MT_SLOT          0
E: 15.954242 0003 0039 0505     # EV_ABS / ABS_MT_TRACKING_ID   505
E: 15.954242 0003 0035 3851     # EV_ABS / ABS_MT_POSITION_X    3851
E: 15.954242 0003 0036 4076     # EV_ABS / ABS_MT_POSITION_Y    4076
E: 15.954242 0003 003a 0034     # EV_ABS / ABS_MT_PRESSURE      34
E: 15.954242 0001 014a 0001     # EV_KEY / BTN_TOUCH            1
E: 15.954242 0003 0000 3851     # EV_ABS / ABS_X                3851
E: 15.954242 0003 0001 4076     # EV_ABS / ABS_Y                4076
E: 15.954242 0003 0018 0034     # EV_ABS / ABS_PRESSURE         34
E: 15.954242 0001 0145 0001     # EV_KEY / BTN_TOOL_FINGER      1
E: 15.954242 0000 0000 0000     # ------------ SYN_REPORT (0) ----------
... (bunch of regular events)...
E: 16.020614 0000 0000 0000     # ------------ SYN_REPORT (0) ----------
E: 16.043601 0003 0035 3873     # EV_ABS / ABS_MT_POSITION_X    3873
E: 16.043601 0003 0036 3903     # EV_ABS / ABS_MT_POSITION_Y    3903
E: 16.043601 0003 003a 0050     # EV_ABS / ABS_MT_PRESSURE      50
E: 16.043601 0003 0035 3032     # EV_ABS / ABS_MT_POSITION_X    3032
E: 16.043601 0003 0036 3832     # EV_ABS / ABS_MT_POSITION_Y    3832
E: 16.043601 0003 003a 0044     # EV_ABS / ABS_MT_PRESSURE      44
E: 16.043601 0003 0000 3032     # EV_ABS / ABS_X                3032
E: 16.043601 0003 0001 3832     # EV_ABS / ABS_Y                3832
E: 16.043601 0003 0018 0044     # EV_ABS / ABS_PRESSURE         44
E: 16.043601 0001 0145 0000     # EV_KEY / BTN_TOOL_FINGER      0
E: 16.043601 0001 014d 0001     # EV_KEY / BTN_TOOL_DOUBLETAP   1
E: 16.043601 0000 0000 0000     # ------------ SYN_REPORT (0) ----------
E: 16.068837 0003 002f 0001     # EV_ABS / ABS_MT_SLOT          1
E: 16.068837 0003 0039 0506     # EV_ABS / ABS_MT_TRACKING_ID   506
E: 16.068837 0003 0035 3912     # EV_ABS / ABS_MT_POSITION_X    3912
E: 16.068837 0003 0036 3743     # EV_ABS / ABS_MT_POSITION_Y    3743
E: 16.068837 0003 003a 0056     # EV_ABS / ABS_MT_PRESSURE      56
E: 16.068837 0003 002f 0000     # EV_ABS / ABS_MT_SLOT          0
E: 16.068837 0003 0035 3026     # EV_ABS / ABS_MT_POSITION_X    3026
E: 16.068837 0003 0036 3708     # EV_ABS / ABS_MT_POSITION_Y    3708
E: 16.068837 0003 003a 0052     # EV_ABS / ABS_MT_PRESSURE      52
E: 16.068837 0003 0000 3026     # EV_ABS / ABS_X                3026
E: 16.068837 0003 0001 3708     # EV_ABS / ABS_Y                3708
E: 16.068837 0003 0018 0052     # EV_ABS / ABS_PRESSURE         52
E: 16.068837 0000 0000 0000     # ------------ SYN_REPORT (0) ----------

Slot 0 and 1 gets inverted in the second report above, which
introduces a cursor jump. The problem is that this cursor jump is
often enough to leave the current widget, and X sends the
scrolling events to whoever is now under the cursor.
Reported-by: Benjamin Tissoires <btissoir@redhat.com>
Reported-by: Hans de Goede <hdegoede@redhat.com>