This reverts commit d7c48980811a82cf4a703a24f4d7a1c7d106090f.
Part of reverting PR #24803 on branch `6.0.x`, because that PR is a
follow-up to PR #19904, which was only merged into master.
PR Close#24809
The reporter was added in 87d56acda, with the purpose of fixing
source-map paths (which was apparently needed back then). Things have
moved around a lot since then and the custom reporter doesn't seem to be
necessary any more. By removing the reporter, we have one less thing to
worry about while upgrading karma; plus we get improvements in built-in
reporters for free.
Output with the custom reporter:
```
at someMethod (packages/core/.../some-file.ts:13:37)
```
Output with the built-in reporter:
```
at someMethod (packages/core/.../some-file.ts:13.37 <- dist/all/@angular/core/.../some-file.js:1:337)
```
PR Close#24803
