Eliminate the fractionalHexLiteralsAreNotSupported diagnostic

[TwitchBronBron]

Let's eliminate this fractionalHexLiteralsAreNotSupported diagnostic entirely. The lexer doesn't do a great job safely detecting this (i.e. it'll show this error for &HFF.asString() (i know it doesn't exist, but still, that's the parser job to say a method doesn't exist), so we shouldn't even show this error (and instead show normal parser errors)

Originally posted by @TwitchBronBron in #1241 (comment)