[css-syntax-3] Remove duplicate token stream creations

[cdoublev]

tokenize maps a stream of code points into a stream of tokens:

To tokenize a stream of code points into a stream of CSS tokens input, repeatedly consume a token from input until an <EOF-token> is reached, pushing each of the returned tokens into a stream.

But a stream of tokens is also created with its result:

• in normalize into a token stream:

3. [...], tokenize the result, then create a new token stream with those tokens as its tokens, and return it.

• in consume the value of a unicode-range descriptor:

1. Let tokens be the result of tokenizing [...]. Let input be a new token stream from tokens.