[Mobile Tracer] Use unified source file list for BUCK build (#84770)
Currently, the source list `torch_mobile_tracer_sources` in `build_variables.bzl` is used only for OSS build. This resulted in a regression for OSS builds when `TRACING_BASED=1` was used to build the OSS model tracer binary. To prevent this from happening in the future, it makes sense to re-use this list for internal BUCK builds as well. This change does that.
#accept2ship
Differential Revision: [D39392010](https://our.internmc.facebook.com/intern/diff/D39392010/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D39392010/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84770
Approved by: https://github.com/cccclai
