Remove all diphthongs from list of sounds

[nya-elimu]

Teaching "gliding vowels" (e.g. /ɔɪ/ or /əʊ/) would only introduce more confusion to a child trying to memorize sound-letter correspondences. For improved pedagogy, we will therefore only be using individual sounds when creating sound-to-letter correspondences.

Update the content for each language:

• http://eng.elimu.ai/content/sound/list
• http://tgl.elimu.ai/content/sound/list
• http://hin.elimu.ai/content/sound/list

Tip

If the sound you will be removing is already being used by a letter-sound correspondence, update the letter-sound correspondence before removing the sound.