tools build: return empty list for mbed2

We cant afford to raise an exception now. As anyone using this out there do not catch it. Rather
an empty list, as it can work after this fix - won't do anything.

Author: 0xc0170

tools/build_api.py

@@ -412,12 +412,12 @@ def get_mbed_official_release(version):
     """
 
     # we ignore version for Mbed 6 as all targets in targets.json file are being supported
-    # if someone passes 2, we return emtpy tuple, if 5, we keep the behavior the same as 
+    # if someone passes 2, we return empty tuple, if 5, we keep the behavior the same as 
     # release version is deprecated and all targets are being supported that are present
     # in targets.json file
 
     if version == '2':
-        raise InvalidReleaseTargetException("Mbed 2 is no longer supported with this version of the tools")
+        return tuple(tuple([]))
 
     mbed_official_release = (
         tuple(