Even though this is an older question, I had the same one myself recently, and came up with a more simple solution using regular expressions and the string replace function as another alternative (no need for external js libraries or reliance on the ECMAScript Internalization API):
var d = new Date();
var localeTime = d.toLocaleTimeString();
var localeTimeSansSeconds = localeTime.replace(/:(\d{2}) (?=[AP]M)/, " ");
This approach uses a regex look-ahead to grab the :ss AM/PM end of the string and replaces the :ss part with a space, returning the rest of the string untouched. (Literally says "Find a colon with two digits and a space that is followed by either AM or PM and replace the colon, two digits, and space portion with just a space).
This expression/approach only works for en-US and en-US-like Locales. If you also wanted a similar outcome with, say, British English (en-GB), which doesn't use AM/PM, a different regular expression is needed.
Based on the original questioner's sample output, I assume that they were primarily dealing with American audiences and the en-US time schema.