Remove dead 'vault_password' play attribute (#41847)

docs/docsite/keyword_desc.yml

@@ -71,5 +71,4 @@ until: "This keyword implies a ':term:`retries` loop' that will go on until the
 vars: Dictionary/map of variables
 vars_files: List of files that contain vars to include in the play.
 vars_prompt: list of variables to prompt for.
-vault_password: Secret used to decrypt vaulted files or variables.
 when: Conditional expression, determines if an iteration of a task is run or not.

lib/ansible/playbook/play.py

@@ -65,7 +65,6 @@ class Play(Base, Taggable, Become):
     # Variable Attributes
     _vars_files = FieldAttribute(isa='list', default=[], priority=99)
     _vars_prompt = FieldAttribute(isa='list', default=[], always_post_validate=True)
-    _vault_password = FieldAttribute(isa='string', always_post_validate=True)
 
     # Role Attributes
     _roles = FieldAttribute(isa='list', default=[], priority=90)