[css-text-3] Clean up errors from shorthanding of text-align. Fixes #2308.

Author: fantasai

css-text-3/Overview.bs

@@ -1362,15 +1362,12 @@ Shaping Across Intra-word Breaks</h3>
 
     <p>This property describes how the last line of a block or a line
       right before a <a>forced line break</a> is aligned.
-      If a line is also the first line of the block
-      or the first line after a <a>forced line break</a>,
-      'text-align-last' takes precedence over 'text-align-all'.
 
     <p>If <dfn dfn-for=text-align-last dfn-type=value>auto</dfn> is specified,
-      content on the affected line is aligned per 'text-align'
-      unless 'text-align' is set to ''justify'',
+      content on the affected line is aligned per 'text-align-all'
+      unless 'text-align-all' is set to ''justify'',
       in which case it is start-aligned.
-      All other values have the same meanings as in 'text-align'.
+      All other values are interpreted as described for 'text-align'.
 
   <h3 id="text-justify-property" caniuse="css-text-justify">
     Justification Method: the 'text-justify' property</h3>