Follow up to #825.

This pull request improves the engine by not compiling `<% # coments %>
comments as part of the template. Outputting `# coments` could lead to
some cases, where the template could be compiled but couldn't be
rendered, because it would comment out important pieces of the template.

```erb
<% if true %><% # comment %><%= "Hello World" %><% end %>
```

**Before**

`exe/herb compile test.html.erb`
```ruby
__herb = ::Herb::Engine; _buf = ::String.new;
 if true; # comment
 _buf << __herb.h(("Hello World")); end; _buf << '
'.freeze;
_buf.to_s
```


**After**

`exe/herb compile test.html.erb`
```ruby
__herb = ::Herb::Engine; _buf = ::String.new;
 if true; _buf << __herb.h(("Hello World")); end; _buf << '
'.freeze;
_buf.to_s
```


### For reference

`bin/erubi-compile test.html.erb`
```ruby
__erubi = ::Erubi; _buf = ::String.new; if true ; # comment ; _buf << __erubi.h(( "Hello World" )); end ; _buf << '
'.freeze;
_buf.to_s
```

`bin/erubi-render test.html.erb`
```
bin/erubi-render:117:in 'Kernel#eval': (eval at bin/erubi-render:117):2: syntax errors found (SyntaxError)
  1 | __erubi = ::Erubi; _buf = ::String.new; if true ; # comment ; _buf << __erubi.h(( "Hello World" )); end ; _buf << '
> 2 | '.freeze;
    | ^ unterminated string meets end of file
  3 | _buf.to_s
> 4 |
    | ^ expected an `end` to close the conditional clause

    | ^ unexpected end-of-input, assuming it is closing the parent top level context

        from bin/erubi-render:117:in 'ErubiRenderer#render_template'
        from bin/erubi-render:31:in 'ErubiRenderer#run'
        from bin/erubi-render:152:in '<main>'
```

`exe/herb render test.html.erb`
```
Hello World
```