Add decode hooks to other parse functions

Now that the original config parsing leaves the opaque maps unmodified
these secondary decodes must use the hooks to normalize fields.

agent/structs/connect_proxy_config.go

@@ -426,8 +426,6 @@ type ExposePath struct {
 	ParsedFromCheck bool
 }
 
-// TODO: this is most likely not used. The API type is the one to be deserialized
-// with JSON
 func (t *ExposePath) UnmarshalJSON(data []byte) (err error) {
 	type Alias ExposePath
 	aux := &struct {

agent/xds/config.go

@@ -58,7 +58,6 @@ type ProxyConfig struct {
 // allows caller to choose whether and how to report the error.
 func ParseProxyConfig(m map[string]interface{}) (ProxyConfig, error) {
 	var cfg ProxyConfig
-	err := mapstructure.WeakDecode(m, &cfg)
 	decodeConf := &mapstructure.DecoderConfig{
 		DecodeHook: mapstructure.ComposeDecodeHookFunc(
 			decode.HookWeakDecodeFromSlice,