artiq_flash: do not suppress useful backtrace information

artiq/frontend/artiq_flash.py

@@ -327,7 +327,6 @@ def main():
         atexit.register(lambda: os.unlink(bin_filename))
         return bin_filename
 
-    try:
     for action in args.action:
         if action == "gateware":
             gateware_bin = convert_gateware(
@@ -365,8 +364,6 @@ def main():
             programmer.start()
         else:
             raise ValueError("invalid action", action)
-    except FileNotFoundError as e:
-        raise SystemExit(e)
 
     if args.dry_run:
         print("\n".join(programmer.script()))