polarssl: remove unmaintained package

polarssl: remove unmaintained package

The 1.2.x branch is no longer maintained, so remove it since it's
likely security-vulnerable.

mbedtls is the modern replacement which was renamed from polarssl when
ARM bought them up.
However major releases broke API so polarssl 1.2.x isn't always
interchangeable with polarssl/mbedtls 1.3.x (interim mixed naming
because of new ownership) or newer 2.x series.

Fortunately we don't have any package in the tree that uses polarssl
exclusively.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[Thomas:
 - Remove entry in DEVELOPERS file for this package. Noticed by Arnout.
 - Remove comment in bctoolbox.mk that no longer makes sense after
   polarssl removal. Noticed by Arnout.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>