Run cbicov with an empty codebase

Using an empty codebase means that cbicov will only generate coverage
information for files in the specified source directory.

Pre-populating the codebase file list restricts our ability to exclude files,
because files that are explicitly listed in the codebase are assumed to have
been specified by the user.

Signed-off-by: John Pennycook <john.pennycook@intel.com>

bin/cbicov

@@ -62,9 +62,8 @@ if __name__ == "__main__":
     # - codebase contains all files in the specified compilation database
     db = config.load_database(dbpath, source_dir)
     configuration = {"cli": db}
-    files = [e["file"] for e in db]
     codebase = {
-        "files": files,
+        "files": [],
         "platforms": ["cli"],
         "exclude_files": [],
         "rootdir": source_dir,