fix(sourcemaps): reduce verbose noise

[JonasBa]

verbose mode logging generates a lot of noise for non sourcemaps files, this PR changes so we outputs logs only when true .js.map sourcemaps are skipped

[markerikson]

Does that check actually do anything? My understanding was that in here we are only getting filenames that are in the sources list, which should always be source filename and not sourcemap names.