fix(genrule): remove quoting of `$(OUTS)`/`$(SRCS)`

As per the documentation for the [predefined variables]:

> If the filenames corresponding to the input labels or the output filenames contain spaces, `'`, or other special characters...then `$(SRCS)` and `$(OUTS)` are not suitable for interpolation into a command line, as they do not have the semantics that `"${@}"` would in Bash.

[predefined variables]: https://bazel.build/reference/be/make-variables#predefined_genrule_variables