EPUB writer: change default accessibilityFeatures.

Don't include ARIA and MathML in general; they won't apply for
epub2 or documents without math.

MANUAL.txt

@@ -6857,8 +6857,6 @@ The following fields are recognized:
     Defaults to
 
         - "alternativeText"
-        - "ARIA"
-        - "MathML"
         - "readingOrder"
         - "structuralNavigation"
         - "tableOfContents"

src/Text/Pandoc/Writers/EPUB.hs

@@ -413,9 +413,8 @@ metadataFromMeta opts meta = EPUBMetadata{
         accessibilityFeatures =
                       case lookupMeta "accessibilityFeatures" meta of
                          Just (MetaList xs) -> map metaValueToString xs
-                         _ -> ["alternativeText","ARIA","MathML",
-                               "readingOrder", "structuralNavigation",
-                               "tableOfContents"]
+                         _ -> ["alternativeText", "readingOrder",
+                               "structuralNavigation", "tableOfContents"]
         accessibilityHazards =
                        case lookupMeta "accessibilityHazards" meta of
                          Just (MetaList xs) -> map metaValueToString xs