Suspicious comparison of strings by reference identity

[sir-wabbit]

https://github.com/lampepfl/dotty/blob/36c2e34bc33a39a41ec383e997185613bf88c64c/compiler/src/dotty/tools/dotc/core/Decorators.scala#L160

[Blaisorblade]

TLDR it looks correct (because strippedName comes from stripSuffix and because of stripSuffix's contract and implementation), but this is subtle enough that we should either add a test or use !=.
Since String.equals happens to be O(1) in this case (because it checks the length before the content), changing the code looks simpler.