translate-c is moving towards a package provided by the build system
(#20630).

The repository https://github.com/ziglang/translate-c/ implements C
translation using Aro. This commit deletes the Aro implementation of C
translation from the Zig repository, leaving only the Clang
implementation.

The other dependency on Aro is for the preprocessor. This must move to
`std.zig.Preprocessor`, be untangled from Aro, and independently
maintained.

There must also be added a Preprocessor Build Step, which this commit
does not do.

Furthermore, the preprocessor must be exposed as a zig compiler JIT
command rather than always being compiled into the compiler. This will
reduce binary size and time spent waiting for zig to build.