Aspect ratio not maintained on small screens for attachments with no thumbnail

[Sesquipedalian]

Description

When image attachment thumbnails are quite large, the thumbnail's aspect ration may be distorted when the thumbnail is viewed on a small device. This is because the width and height attributes are set on the thumbnail, but then CSS sets max-width: 100% on it.

Steps to reproduce

1. Enable attachment thumbnails and set the thumbnail size to something quite large, e.g. 1000 x 1000.
2. Attach a large image to a post.
3. View the post on a small device.

Environment (complete as necessary)

• Version/Git revision:
• Database Type:
• Database Version:
• PHP Version:

Additional information/references

To fix this, all we need to do is remove the height="' . $attachment['height'] . '" bit from this line:
https://github.com/SimpleMachines/SMF2.1/blob/b9e3b273aa8c1dcdde424dfb751e65bd223f2d4c/Themes/default/Display.template.php#L786

[albertlast]

would be not better to maintaine the aspect ratio?
https://css-tricks.com/almanac/properties/a/aspect-ratio/

[Sesquipedalian]

By default, the browser will maintain the image's inherent aspect ratio. It only overrides the inherent aspect ratio if we set both the width and height values.

[jdarwood007]

Related to #6541?