Revert "clang/test/Driver/crash-report.c: This requires rewriter for -frewrite-includes. [PR20321]"

We've decided to make the core rewriter class and PP rewriters mandatory.
They're only a few hundred lines of code in total and not worth supporting as a
distinct build configuration, especially since doing so disables key compiler
features.

This reverts commit r213150.

Revert "clang/test: Introduce the feature "rewriter" for --enable-clang-rewriter."

This reverts commit r213148.

Revert "Move clang/test/Frontend/rewrite-*.c to clang/test/Frontend/Rewriter/"

This reverts commit r213146.