flac: bump to version 1.3.1

All patches upstream and add hash file.

[Thomas: remove AUTORECONF = YES, since we no longer have any
patches touching configure.ac/Makefile.am]

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>