etc: licenseck: don't hardcode a specific year
auto merge of #11314 : adridu59/rust/patch-license, r=brson

- don't check for an hardcoded copyright claim year, check the 2 surrounding strings instead
- logic: if either the `//` or `#`-style copyright patterns are found, don't invalidate
- cleanup hardcoded content and streamline the few files with different line breaks

r? @brson