endpoint.hpp throws a compiler warning due to `const bool` return

[Nehal Patel]

https://github.com/zeromq/libzmq/blame/814dab58a4eea3202d28d7db4fa24c27287c5378/src/endpoint.hpp#L32

Since bool is returned by value, the const is redundant and will throw an ignored-qualifier warning with clang:

[build] build/host/_deps/zeromq-src/src/endpoint.hpp:32:5: warning: 'const' type qualifier on return type has no effect [-Wignored-qualifiers]
[build]    32 |     const bool clash () const { return local == remote; }
[build]       |     ^~~~~