Feat: remove default variable assignation (p)

The variable p was accidentally mapped to a Player due to init logic.
This commit removes the reference so users are not wondering what this
magical variable is.

sardine_core/run.py

@@ -108,6 +108,7 @@
     p = Player(name=player)
     globals()[player] = p
     bowl.add_handler(p)
+    del p
 
 # Extensions
 # An extension configuration file contains the following fields: