[vm/corelib] Remove unnecessary isEmpty call from List._fromLiteral
[vm/corelib] Remove unnecessary isEmpty call from List._fromLiteral

VM doesn't call List._fromLiteral for empty list literals, so there is
no need in testing if elements are empty in List._fromLiteral.

Also, List._fromLiteral is always called on _List elements, so we can
use a more specific type for its parameter.

Fixes https://github.com/dart-lang/sdk/issues/44393

Change-Id: I2e58534c6d183c30673a68bc6705f5c64edc9f09
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175280
Reviewed-by: Stephen Adams <60cb5b73b7e0cb7dcda53302da4fab6ecfc7fa8b@google.com>
Commit-Queue: Alexander Markov <239e774fd29abc1267878f57afe1a8a03e0ca887@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk