package/gcc: remove version 5.5.5

gcc 9.2 is around, gcc 8.4 is the default version, so drop
5.5 in order to reduce the gcc choice.

GCC 5.5 was disabled for Glibc based toolchain since Glibc
2.30 needs GCC 6.2 or later.

See:
https://sourceware.org/ml/libc-alpha/2019-08/msg00029.html



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>