[runtimes] Remove the ability to select the old libc++ testing format

As announced on libcxx-dev at [1], the old libc++ testing format is being
removed in favour of the new one. Follow-up commits will clean up the
code that is dead after the removal of this option.

[1]: http://lists.llvm.org/pipermail/libcxx-dev/2020-June/000885.html

GitOrigin-RevId: 5d838808854b9b6a7cb357d7768d37fc94fa7d73
diff --git a/test/lit.site.cfg.in b/test/lit.site.cfg.in
index 4c8d420..3d1c546 100644
--- a/test/lit.site.cfg.in
+++ b/test/lit.site.cfg.in
@@ -54,15 +54,11 @@
 # Infer the test_exec_root from the build directory.
 config.test_exec_root = os.path.join(config.libcxxabi_obj_root, 'test')
 
+import libcxx.test.newformat
+config.test_format = libcxx.test.newformat.CxxStandardLibraryTest()
+
 lit_config.note('Using configuration variant: libcxxabi')
 import libcxxabi.test.config
 configuration = libcxxabi.test.config.Configuration(lit_config, config)
 configuration.configure()
 configuration.print_config_info()
-if lit_config.params.get('use_old_format', False):
-    lit_config.note("Using the old libc++ testing format")
-    config.test_format = configuration.get_test_format()
-else:
-    lit_config.note("Using the new libc++ testing format")
-    import libcxx.test.newformat
-    config.test_format = libcxx.test.newformat.CxxStandardLibraryTest()