Xcode Simulator: how to remove older unneeded devices?
In Xcode 6+ you can simply go to Menu > Window > Devices > Simulators and delete a simulator you don't need.
Did you try to just delete the 4.3 SDK from within the Xcode Package?
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs
please also delete the corresponding .dmg file in
~/Library/Caches/com.apple.dt.Xcode/Downloads
to prevent Xcode from re-installing the same package again.
for XCode >= 6 see @praveen-matanam 's answer
In Xcode 6 and above, you can find and delete the simulators from the path /Library/Developer/CoreSimulator/Profiles/Runtimes
. Restart Xcode in order to take effect (may not be needed).