Strip preprocessor lang attribute from output

Is your feature request related to a problem? Please describe. svelte-preprocess utilizes the lang attribute to identify the languages used, but leaves them in the output after preprocessing.

Describe the solution you'd like I would like the lang attribute to be removed from the generated output, primarily for cleanliness.

How important is this feature to you? Not important at all, but seems like something that should be done, and should be done here.

Additional context Originally noticed by bluwy