Remove expired certificates from selection in bookmark window

[minfrin]

Describe the bug
When viewing the dropdown of certificates in the bookmark screen in Mountain Duck, the list of certificates includes all expired certificates in the keychain in addition to current ones.

This makes it difficult to choose the correct certificate, as there is no clue as to which cert is which.

To Reproduce
Steps to reproduce the behavior:

1. Open a bookmark.
2. Click the dropdown on "client certificates"
3. See long list of certificates, including expired certs, with no way to tell which is which.

Expected behavior
Only valid non-expired certificates should appear in the dropdown list.

Screenshots

Desktop (please complete the following information):

• OS: MacOS
• Version 4.16.3 (22374)