message: refactor(compiler): use `DefinitionMap` and remove `mapToMapExpression()`
  By consistently using the `DefinitionMap` class there is no longer
  any need for the `mapToMapExpression()` function.
  PR Close
diff: @@ -11,21 +11,6 @@ import {escapeIdentifier} from '../output/abstract_emitter';
  import * as o from '../output/output_ast';
  import {OutputContext} from '../util';
  -/**
  - * Convert an object map with `Expression` values into a `LiteralMapExpr`.
  - */
  -export function mapToMapExpression(map: {[key: string]: o.Expression|undefined}): o.LiteralMapExpr {
  - const result = Object.keys(map).map(
  - key => ({
  - key,
  - // The assertion here is because really TypeScript doesn't allow us to express that if the
  - // key is present, it will have a value, but this is true in reality.
  - value: map[key]!,
  - quoted: false,
  - }));
  - return o.literalMap(result);
  -}
  -
  /**
  * Convert metadata into an `Expression` in the given `OutputContext`.
  *
  