net/asterisk*: Remove ONLY_FOR_ARCHS restriction

There is no architecture specific code in asterisk. It used to have
problems building on certain architectures due to the software
leveraging some then advanced compiler features.

At present asterisk is expected to compile and work fine on all
supported architectures. This is also shown by the restriction being
removed including almost all of them.

Noticed by: danfe
MFH: 2021Q3