Angular 5.0+ has a full peer dependencies setup (with 6.0+ also having a configurable runtime error check) to ensure that an appropriate version of typescript is available for compilation. Angular CLI 8.0+ does not support Angular versions prior to these and therefore the warning is redundant. For the case where the developer wishes to use an unsupported TypeScript version, the developer would need to adjust two similar but differently name settings in two different configuration files.
This should clean up the code a bit.
Note: at first I added the no-useless-cast rule, but after getting frustrated
with it (as it has many false positive), I decided to remove the rule but some
useless casts were removed so I let those in the PR.
