updated flowchart.js to 1.14.2 (#671)

using types from the package instead of our own

src/external-types/flowchart.js/index.d.ts

@@ -1,13 +0,0 @@
-declare module 'flowchart.js' {
-  type Options = {
-    'line-width': number,
-    'fill': string,
-    'font-size': string,
-    'font-family': string
-  }
-  type ParseOutput = {
-    clean: () => void,
-    drawSVG: (container: HTMLElement, options: Options) => void,
-  }
-  export const parse: (code: string) => ParseOutput
-}