Revert "Return error when TmplText errors in sns notifier"

[gotjosh]

Reverts #3531

[gotjosh]

@TheMeier this did break the tests - Let's revert it for now until I have some time to figure out what's wrong?

[grobinson-grafana]

There are two imports for error package with the same name:

package sns

import (
	"errors"
	...

	"github.com/pkg/errors"
)

`errors` redeclared in this block (typecheck)

see 603a728.

[grobinson-grafana]

We should also replace errors.Wrap with fmt.Errorf 🙂 @emanlodovice

[emanlodovice]

My apologies for the previous PR, it was old and needed to be rebase. I have opened a new PR to fix the issue #3879 . Please have a look. Thank you.