Enable default cetl::pmr::PmrInterfaceDeleter ctor.

[serges147]

Without this I cannot have by default empty unique ptr member, like:

struct Xxx {

private:
    UniquePtr<ITxSocket> tx_socket_ptr_;
};

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
69.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud