brltty: bump to version 5.6

brltty: bump to version 5.6

- Remove first, second and third patch (already in version)
- Fix major/minor build failure with glibc 2.28, see:
  https://github.com/brltty/brltty/commit/cee581fac78d29bdf9acb6d1378cf4d005ff3afd
- Update web site URL to brltty.app, see
  https://github.com/brltty/brltty/commit/97efaecd6cfb665c0b5f0ac8ec69416618d45635
- Update license to LPGL-2.1+, see:
  https://github.com/brltty/brltty/commit/16ccb7d13f018e7557633a24fc02866b85871fa0

Fixes:
 - http://autobuild.buildroot.org/results/0fb2c33f00990e471736c4180f23026fa9adb982

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>