Only show the first (relevant) remove hint in excuses

In the unlike case that there are multiple removal hints, showing
the first valid hint should be sufficient.

Signed-off-by: Niels Thykier <niels@thykier.net>

britney.py

@@ -1304,6 +1304,7 @@ class Britney(object):
                 excuse.addhtml("Removal request by %s" % (hint.user))
                 excuse.addhtml("Trying to remove package, not update it")
                 excuse.is_valid = False
+                break
 
         # check if there is a `block' or `block-udeb' hint for this package, or a `block-all source' hint
         blocked = {}