refactor(consts): remove unused legacy era constants

Remove the legacy era constants (SHELLEY, ALLEGRA, MARY, ALONZO, BABBAGE)
from the CommandEras class in consts.py. Only CONWAY and LATEST are now
retained, reflecting current usage and simplifying the codebase.

Author: mkoura

cardano_clusterlib/consts.py

@@ -14,11 +14,6 @@
 
 
 class CommandEras:
-    SHELLEY: tp.Final[str] = "shelley"
-    ALLEGRA: tp.Final[str] = "allegra"
-    MARY: tp.Final[str] = "mary"
-    ALONZO: tp.Final[str] = "alonzo"
-    BABBAGE: tp.Final[str] = "babbage"
     CONWAY: tp.Final[str] = "conway"
     LATEST: tp.Final[str] = "latest"