Remove content and related fields from boosts (#3131)

These duplicate the content of the target and aren't necessary for anything.

- Stops copying some fields from target when boosting or processing a remote boost
- Adds a migration to null out existing duplicate data
- Updates tests

testrig/testmodels.go

@@ -1488,8 +1488,6 @@ func NewTestStatuses() map[string]*gtsmodel.Status {
 			ID:                       "01G36SF3V6Y6V5BF9P4R7PQG7G",
 			URI:                      "http://localhost:8080/users/admin/statuses/01G36SF3V6Y6V5BF9P4R7PQG7G",
 			URL:                      "http://localhost:8080/@admin/statuses/01G36SF3V6Y6V5BF9P4R7PQG7G",
-			Content:                  "hello everyone!",
-			Text:                     "hello everyone!",
 			CreatedAt:                TimeMustParse("2021-10-20T12:41:37+02:00"),
 			UpdatedAt:                TimeMustParse("2021-10-20T12:41:37+02:00"),
 			Local:                    util.Ptr(true),
@@ -1501,10 +1499,8 @@ func NewTestStatuses() map[string]*gtsmodel.Status {
 			BoostOfID:                "01F8MHAMCHF6Y650WCRSCP4WMY",
 			BoostOfAccountID:         "01F8MH1H7YV1Z7D2C8K2730QBF",
 			ThreadID:                 "",
-			ContentWarning:           "introduction post",
 			Visibility:               gtsmodel.VisibilityPublic,
-			Sensitive:                util.Ptr(true),
-			Language:                 "en",
+			Sensitive:                util.Ptr(false),
 			CreatedWithApplicationID: "01F8MGXQRHYF5QPMTMXP78QC2F",
 			Federated:                util.Ptr(true),
 			ActivityStreamsType:      ap.ObjectNote,