Avoid stripping debug symbols from C++ unit tests in Evergreen

As part of SERVER-20315, running the C++ unit tests was split out into its own unittests task. This required changes to strip the C++ unit tests, tar them up, and upload them to S3.

With the changes from SERVER-25691, we'll now have a separate compile_all task that builds everything including the C++ unit tests. Our JavaScript integration tests (e.g. jsCore_WT) will continue to depend on the compile task that builds everything except the C++ unit tests. This means we can go back to a model where compile_all also runs the C++ unit tests, which brings the following benefits:

• We won't need to package up the C++ unit tests and upload them to S3.
• We won't strip the C++ unit tests to save space and will be able to run them with symbols intact to make debugging easier.