Unable to delete intention: Sources[0].LegacyMeta must be omitted

#### Overview of the Issue

I am trying to delete an intention, but I'm receiving an error message a 500 response with the error message, `Sources[0].LegacyMeta must be omitted`.

Additionally it seems that if an intention has any metadata assigned, it may not be updated by the UI returning the message, `error="Meta must not be specified, or should be unchanged during an update."`

#### Reproduction Steps

Steps to reproduce this issue, eg:

Unsure, it may be because this intention was defined when the cluster was 1.6.2 or so.

1. Have a legacy intention defined
2. Upgrade to 1.9.3
3. Attempt to edit or delete the intention

### Consul info for both Client and Server

Server info

```
agent:
check_monitors = 0
check_ttls = 0
checks = 0
services = 0
build:
prerelease =
revision = f55da930
version = 1.9.3
consul:
acl = enabled
bootstrap = false
known_datacenters = 3
leader = true
leader_addr = 10.70.253.191:8300
server = true
raft: applied_index = 115592433
commit_index = 115592433
fsm_pending = 0
last_contact = 0
last_log_index = 115592433
last_log_term = 12000
last_snapshot_index = 115582181
last_snapshot_term = 12000
latest_configuration = [{Suffrage:Voter ID:ea967cb2-b51d-2f71-0125-46c36f76a31b Address:10.70.253.191:8300} {Suffrage:Voter ID:e506af7d-2919-d83c-610f-18f9e3992bf7 Address:10.70.252.184:8300} {Suffrage:Voter ID:404b58d0-ddfd-9aaf-d082-c0d84676f9
e6 Address:10.70.253.208:8300}]
latest_configuration_index = 0
num_peers = 2
protocol_version = 3
protocol_version_max = 3
protocol_version_min = 0
snapshot_version_max = 1
snapshot_version_min = 0
state = Leader
term = 12000
runtime:
arch = amd64
cpu_count = 2
goroutines = 1105
max_procs = 2
os = linux
version = go1.15.6
serf_lan:
coordinate_resets = 0
encrypted = true
event_queue = 0
event_time = 2151
failed = 0
health_score = 0
intent_queue = 0
left = 2
member_time = 29313
members = 146
query_queue = 0
query_time = 4
serf_wan:
coordinate_resets = 0
encrypted = true
event_queue = 0
event_time = 1
failed = 0
health_score = 0
intent_queue = 0
left = 0
member_time = 6205
members = 9
query_queue = 0
query_time = 1
```

### Operating system and Environment details

CentOS 7 x86_64

### Log Fragments

```
Feb 23 16:38:48 qachi-inf-001.tw-test.net consul[47687]: 2021-02-23T16:38:48.898-0600 [ERROR] agent.http: Request error: method=DELETE url=/v1/connect/intentions/exact?source=default%2Freporting-service&destination=default%2Fportal-stats-service&dc=qachi from=127.0.0.1:43782 error="Sources[0].LegacyMeta must be omitted"
Feb 23 16:38:48 qachi-inf-001.tw-test.net consul[47687]: 2021-02-23T16:38:48.898-0600 [DEBUG] agent.http: Request finished: method=DELETE url=/v1/connect/intentions/exact?source=default%2Freporting-service&destination=default%2Fportal-stats-service&dc=qachi from=127.0.0.1:43782 latency=10.176312ms
```

Intention information:
```
{
"CreatedAt": "2020-12-03T19:25:08.604552657Z",
"UpdatedAt": "2020-12-03T19:25:08.604552657Z",
"ID": "adca4769-879b-c047-335f-765a552ecbd4",
"SourceNS": "default",
"SourceName": "reporting-service",
"DestinationNS": "default",
"DestinationName": "portal-stats-service",
"SourceType": "consul",
"Action": "allow",
"Precedence": 9,
"Hash": "AhONHPeHzoKaT0/Rz8qb+IED+Cn+nFG9QLw1tJm/Bx0=",
"CreateIndex": 115235406,
"ModifyIndex": 115585886
}
```