Checking my list of alternative launchers, it looks like Launcher+ should fit your needs. Quotes from its description answer your listed requirements:
- Just like the normal AOSP launcher: compiled straight from AOSP
- just without the bar and without Google Now: Hide the Google Search Bar
- Nexus 5: guaranteed to work on the Nexus 4 and 5 (and yes, I know about the special issue with those devices concerning the search bar – so this is the master criterium)
Unfortunately, the description doesn't mention a license (and no homepage to check with), so I must pass on that requirement. At least it "ships at no charge", and is available at Google Play.
Screenshots prove: Searchbar is there, but can be hidden (Source: Google Play; click to enlarge)
I have not used this app myself, so I cannot vouch for it from personal experience. Play store rating is 4 stars at almost 6k votes, so it cannot be that bad. And one of your criteria seems to be only met partly: Maintained to follow closely new upstream developments – there wasn't any update lately to this launcher. Still, if you want to get rid of the search bar on your N5, it should be a good choice.
Alternatives you might wish to take a look at (not mentioning all your requirements, but according to the screenshots and "reading between the lines" might be a close fit as well):
- Polaris Launcher: More up-to-date. According to the screenshots, you can disable the search bar – which is explicitely mentioned (just found it): Hide or move the position of individual desktop elements (search bar, dock, page indicator). The N5 is not explicitely mentioned. Comes in a free version with in-app-payment to go Pro.
- Kcin Launcher is based on AOSP, and a little more up-to-date. Doesn't mention search bar hiding, but screenshots might indicate that (the sentence Highly customizable, with many useful settings could mean anything ;) No license mentioned here either.