Remove extra ddtrace source files.

[purple4reina]

What does this PR do?

Removes \*.c \*.cpp \*.cc \*.h \*.hpp \*.pyx files from ddtrace during build.

Motivation

When building ddtrace from a branch, it does not perform all the build steps that it would when publishing to PyPI. A missing step is to remove extra source files.

Testing Guidelines

Make sure integration tests pass.

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)