remove deprecated onerror option from readme

Author: Conduitry

README.md

@@ -105,7 +105,6 @@ The Svelte compiler optionally takes a second argument, an object of configurati
 | `globals` | `object`, `function` | When outputting to the `'umd'`, `'iife'` or `'eval'` formats, an object or function mapping the names of imported dependencies to the names of global variables. | `{}` |
 | `preserveComments` | `boolean` | Include comments in rendering. Currently, only applies to SSR rendering | `false` |
 | | | |
-| `onerror` | `function` | Specify a callback for when Svelte encounters an error while compiling the component. Passed two arguments: the error object, and another function that is Svelte's default onerror handling. | (exception is thrown) |
 | `onwarn` | `function` | Specify a callback for when Svelte encounters a non-fatal warning while compiling the component. Passed two arguments: the warning object, and another function that is Svelte's default onwarn handling. | (warning is logged to console) |
 
 ### Preprocessor options