fix incorrect text for Light Crystals, fix Plain Egg pluralisation, remove excess word

For questEggHuntCollectPlainEgg, I've pluralised the text (Plain Eggs) because that reads better in the messages it appears in (and plurals are used in questEvilSanta2CollectTracks and questEvilSanta2CollectBranches).

For questRatCompletion, I've removed "out" from this: "we let out down our guard"
Merge pull request #211 from Alys/questFix

fix incorrect text for Light Crystals, fix Plain Egg pluralisation, remove excess word