Revert "Bluetooth: compute LE flow credits based on recvbuf space"

This reverts commit 632b63f1 which is
commit ce60b923 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: I6685f67d86c6def437924a4e4bc2bdb88d55024c
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>