Revert "Bluetooth: L2CAP: copy RX timestamp to new fragments"

This reverts commit 8c7bfb61 which is
commit 3908feb1 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Id8e36cd9dc828f42be27fb8ce27b53c9843fcdef
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>