std: clean up debug stderr variables
std: clean up debug stderr variables

  - stderr_file_writer was unused
  - stderr_stream was a pointer to a stream, rather than a stream
  - other functions assumed that getStderrStream has already been called

andrewrk/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig