exported: comment starting with "Deprecated:” should be ignored when checking if a comment is present

[ccoVeille]

// Foo does the magic
func Foo() {}

// Bar is blah blah
//
// Deprecated: use Foo
func Bar() {}

//nolint:whatever
func Baz() {}

// Deprecated: is deprecated
func Qux() {}

func Quux() {}

The first two are valid

The third one is fixed by a previous PR:

• fix "exported" rule: invalid message reported for directive comment #1209

And is now reported as: "exported func Baz should have comment or be unexported"

The last one is reported as: "exported func Quux should have comment or be unexported"

The issue is with Qux, the error reported is "comment should be like Qux ...", but in fact here it should be "exported function should have a comment", the very same way Baz is reported

[ccoVeille]

Reminder:

nit: in the next PR please add a comment explaining that .Text removes directives from the comment block
Originally posted by @chavacava in #1209 (comment)

[chavacava]

@ccoVeille , the proposal LGTM.