Remove useless Meta-Action

Some Python class and packages need to be renamed
for a better compliance with the shared terminology
which provides a better understanding of Watcher objects
and components by every contributor.

Partially implements: blueprint glossary-related-refactoring

Change-Id: Ie0e33562f5e990c264a50ab3f533cfa62eac1d19

watcher/common/exception.py

@@ -297,7 +297,3 @@ class VMNotFound(WatcherException):
 
 class HypervisorNotFound(WatcherException):
     message = _("The hypervisor could not be found")
-
-
-class MetaActionNotFound(WatcherException):
-    message = _("The Meta-Action could not be found")