lint: add unnecessary brackets checker

[fexolm]

We need to add checker which will find the errors described below.

• var _ [n](*int) ===>> var _ [n]*int
• *(name).field ===>> name.field (moved to lint: add underef checker #14.)
• var _ (func()) ===>> var _ func()
• func(...) (...) ===>> func(...) ...
• (*a)[i] where a is an array (moved to lint: add underef checker #14.)

[quasilyte]

You can start with a simplest case: fix function result types.
This way, you can concentrate on parenthesis elimination instead of type expression seeking.
Then you can expand the scope to more type expressions.

[quasilyte]

There is also (*a)[i] where a is an array (not a slice).

[quasilyte]

Do we need astutil?
https://github.com/golang/tools/blob/master/go/ast/astutil/util.go#L6

[fexolm]

Function output parameters check is done in #22.
Variable type check is done in #31

[fexolm]

Checks 2 and 5 moved to #14.