Revert max-width styles on caption shortcodes.

This is a partial revert of [41724], so image captions include an
inline `width` style instead of `max-width`.

This returns the caption shortcode to the pre-4.9.0 behavior, while
retaining the extra unit test coverage added in [41724].

Fixes #43123. See #33981.


git-svn-id: https://develop.svn.wordpress.org/trunk@42837 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/shortcode.php

@@ -535,7 +535,7 @@ EOF;
 			),
 			array(
 				'[caption caption="test" width="2"]<div>hello</div>[/caption]',
-				'<div style="max-width: 12px" class="wp-caption alignnone"><div>hello</div><p class="wp-caption-text">test</p></div>',
+				'<div style="width: 12px" class="wp-caption alignnone"><div>hello</div><p class="wp-caption-text">test</p></div>',
 			),
 			array(
 				'<div [gallery]>',