removes type-checking from empty-block rule

[chavacava]

Closes #416

Updated tests but as described in #424 we are currently incapable of testing on confidence level.
I've did some manual testing.

# set confidence = 1 in config, then
$ ./revive -config ./defaults.toml testdata/empty-block.go 
testdata/empty-block.go:13:2: this block is empty, you can remove it
testdata/empty-block.go:18:19: this block is empty, you can remove it
testdata/empty-block.go:26:9: this block is empty, you can remove it
testdata/empty-block.go:30:26: this block is empty, you can remove it
testdata/empty-block.go:34:6: this block is empty, you can remove it

# set confidence = 0.9 in config, then
$ ./revive -config ./defaults.toml testdata/empty-block.go 
testdata/empty-block.go:13:2: this block is empty, you can remove it
testdata/empty-block.go:18:19: this block is empty, you can remove it
testdata/empty-block.go:26:9: this block is empty, you can remove it
testdata/empty-block.go:30:26: this block is empty, you can remove it
testdata/empty-block.go:34:6: this block is empty, you can remove it
testdata/empty-block.go:40:2: this block is empty, you can remove it
testdata/empty-block.go:44:2: this block is empty, you can remove it