Revert "Update XPutBackEvent() to support clients that put back unpadded events"

This reverts commit d6d6cba9.

The reverted commit intended to fix the problem where an unpadded X
event struct is passed into XPutBackEvent, by creating a padded struct
with _XEventToWire and _XWireToEvent. However, _XWireToEvent updates the
last sequence number in Display, which may cause xlib to complain about
lost sequence numbers.

IMO, the problem that commit tried to solve is a bug in the client
library, and workaround it inside Xlib is bad practice, especially given
the problem it caused. Plus, the offender cited in the original commit
message, freeglut, has already fixed this problem.

Fixes: #176 #174

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>