clean: remove redundant `allImportedFiles` check in `_onwrite` (#346)
clean: remove redundant `allImportedFiles` check in `_onwrite` (#346)

- this checks if any of the files in `parsedConfig.fileNames` are _not_
  in `allImportedFiles`, but all the files in `parsedConfig.fileNames`
  are explicitly added in the `options` hook on line 98
  - so this is redundant / dead code; the check will never be true

- this can be considered a remnant of an old bug as an old commit fixed
  a bug with `allImportedFiles` after it was released:
  https://github.com/ezolenko/rollup-plugin-typescript2/commit/f24359e668324124a2de40f955a0ff206bf2cf86
ezolenko/rollup-plugin-typescript2,ezolenko/rollup-plugin-typescript2