PLT-6217 Fixes system message posted to Town Square when a member leaves a team (#7752)

* Fixes system message posted to Town Square when adding/removing team member (#6483)

Fixes unit test method call to match RemoveUserFromTeam modification (#6483)

Fixes system message posted to Town Square when adding/removing team member (#6483)

Removes unnessary error message

* Updates system message when a user leaves a team (#6483)

* Changes system message when a user is removed from team (#6483)

* Adds a new string to be post to town-square when a member is added to a team (#6483)

i18n/en.json

@@ -2166,6 +2166,10 @@
     "id": "api.system.go_routines",
     "translation": "The number of running goroutines is over the health threshold %v of %v"
   },
+  {
+    "id": "api.team.add_user_to_team.added",
+    "translation": "%v added to the team by %v"
+  },
   {
     "id": "api.team.add_user_to_team.missing_parameter.app_error",
     "translation": "Parameter required to add user to team."
@@ -2274,6 +2278,10 @@
     "id": "api.team.is_team_creation_allowed.disabled.app_error",
     "translation": "Team creation has been disabled. Please ask your systems administrator for details."
   },
+  {
+    "id": "api.team.leave.left",
+    "translation": "%v left the team."
+  },
   {
     "id": "api.team.is_team_creation_allowed.domain.app_error",
     "translation": "Email must be from a specific domain (e.g. @example.com). Please ask your systems administrator for details."
@@ -2286,6 +2294,10 @@
     "id": "api.team.permanent_delete_team.deleted.warn",
     "translation": "Permanently deleted team %v id=%v"
   },
+  {
+    "id": "api.team.remove_user_from_team.removed",
+    "translation": "%v was removed from the team."
+  },
   {
     "id": "api.team.remove_user_from_team.missing.app_error",
     "translation": "The user does not appear to be part of this team."