Fix Quenya [[aI]] phoneme

We used to inherit it from the Latin phonemes, which, as I noted in the
commit adding the Sindarin diphthongs, sounds more like /ae/ than /ai/.
Copy the phoneme from Sindarin so that it sounds like /ai/, not /ae/.
(There is no ⟨ae⟩ diphthong in Quenya, so we don’t need a copy of that.)

phsource/ph_quenya

 endphoneme
 
 
+phoneme aI
+  vwl starttype #a endtype #i
+  length 240
+  FMT(vdiph/ai)
+endphoneme
+
 phoneme ui
   vwl starttype #u endtype #i
   length 270