Move overrides for registrations to debug.

These are only useful at INFO if you're worried about accidentally overwriting existing aliases... but even in that case, it's unlikely for overwriting two similar-named but differently-typed to "just work". You kind of _have_ to do it intentionally.

Reviewed at https://rbcommons.com/s/twitter/r/2023/

src/python/pants/base/build_configuration.py

@@ -66,7 +66,7 @@ def register_target_alias(self, alias, target):
                       'given {0}'.format(target))
 
     if alias in self._target_aliases:
-      logger.info('Target alias {alias} has already been registered.  Overwriting!'
+      logger.debug('Target alias {alias} has already been registered. Overwriting!'
                   .format(alias=alias))
     self._target_aliases[alias] = target
     self.register_addressable_alias(alias, target.get_addressable_type())
@@ -82,7 +82,7 @@ def register_exposed_object(self, alias, obj):
                       'via `register_target_alias`'.format(obj))
 
     if alias in self._exposed_objects:
-      logger.info('Object alias {alias} has already been registered.  Overwriting!'
+      logger.debug('Object alias {alias} has already been registered. Overwriting!'
                   .format(alias=alias))
     self._exposed_objects[alias] = obj
 
@@ -99,7 +99,7 @@ def register_addressable_alias(self, alias, addressable_type):
     of the type of instance it yields.
     """
     if alias in self._addressable_alias_map:
-      logger.info('Addressable alias {alias} has already been registered.  Overwriting!'
+      logger.debug('Addressable alias {alias} has already been registered. Overwriting!'
                   .format(alias=alias))
     self._addressable_alias_map[alias] = addressable_type
 
@@ -115,7 +115,7 @@ def register_exposed_context_aware_object_factory(self, alias, context_aware_obj
                       .format(factory=context_aware_object_factory))
 
     if alias in self._exposed_context_aware_object_factories:
-      logger.info('This context aware object factory alias {alias} has already been registered. '
+      logger.debug('This context aware object factory alias {alias} has already been registered. '
                   'Overwriting!'.format(alias=alias))
 
     if callable(context_aware_object_factory):