Fix and enable tfproviderlint R003 check: Remove extraneous Exists functions

[ryndaniels]

Description

As per tfproviderlint check R003, we want to remove extraneous Exists functions from resources. This logic can be handled inside Read functions instead to prevent duplication.

Failing example:

func resourceExampleThingExists(d *schema.ResourceData, meta interface{}) (bool, error) { /* ... */ }

func resourceExampleThingRead(d *schema.ResourceData, meta interface{}) error { /* ... */ }

&schema.Resource{
    Exists: resourceExampleThingExists,
    Read:   resourceExampleThingRead,
    /* ... */
}

Should become:

func resourceExampleThingRead(d *schema.ResourceData, meta interface{}) error { /* ... */ }

&schema.Resource{
    Read: resourceExampleThingRead,
    /* ... */
}

Definition of Done

• In GNUmakefile, add -R003 to tfproviderlint command under lint target and have TravisCI testing pass

[ewbankkit]

After all the linked PRs are merged we can enable R003 in GNUmakefile.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!