Revert "FIX: Decline attribute values core can only quote lossily"

This reverts commit 78ede37.

Guarding it took a serialize-then-inspect call to find out whether core
had dropped the quote characters, for a value that has to contain one
character from each of the nine quotation pairs to get there. Reachable
content is already covered.

Author: renato

assets/javascripts/discourse/lib/rich-editor-extension.js

@@ -100,14 +100,9 @@ function inlineMarkFor(token, schema) {
   return null;
 }
 
+// a bbcode tag is a single line, so no quoting can hold a newline
 function serializableAttr(value) {
-  if (!value || value.includes("\n")) {
-    return null;
-  }
-
-  // with every quote pair used up core drops the quote characters instead of
-  // failing, so check the value survives rather than let it change silently
-  return serializeBBCodeAttr(value, "").includes(value) ? value : null;
+  return value && !value.includes("\n") ? value : null;
 }
 
 // a mark set holds one per type: an identical nesting adds nothing, a differing

test/javascripts/integration/rich-editor-extension-test.js

@@ -304,12 +304,6 @@ module(
         '<p>An <a name="O\'Brien x">anchor</a> here</p>',
         'An [aname="O\'Brien x"]anchor[/aname] here',
       ],
-      // no quote pair is left to wrap it, and dropping the quote characters
-      // would change the value
-      "pasted unquotable aname html is not claimed": [
-        '<p>An <a name="a &quot;\'«”’„‹ b">anchor</a> here</p>',
-        "An anchor here",
-      ],
       "pasted quoted jumpto html": [
         '<p>go <a href="#tar\'get">here</a> now</p>',
         "go [jumpto=tar'get]here[/jumpto] now",