Remove the superfluous build requirement of libsodium-devel

[viciious]

The following lines in the .spec file ensure that the necessary packages are present on the system in case the rpm is being built with libsodium support enabled:

%bcond_with libsodium
%if %{with libsodium}
BuildRequires:  libsodium-devel
%define SODIUM yes
%else
%define SODIUM no
%endif

%{?_with_libsodium:BuildRequires: libsodium-devel}
%{?_with_libsodium:Requires: libsodium}

Unconditionally requiring libsodium-devel makes it impossible to build the spec file with default arguments if the aforementioned package is not installed. This merge request amends that.

[bluca]

Thanks for the PR - please add a commit with a relicense statement https://github.com/zeromq/libzmq/blob/master/RELICENSE/README.md

[viciious]

Thanks for the PR - please add a commit with a relicense statement https://github.com/zeromq/libzmq/blob/master/RELICENSE/README.md

Done