Renamed TestRdar12991846 to the more descriptive TestUnicodeLiterals.

Test cases should not be named after PR or Radar numbers.  It's fine to
annotate them with these numbers in comments, however.

llvm-svn: 260699

lldb/packages/Python/lldbsuite/test/lang/cpp/unicode-literals/TestUnicodeLiterals.py

@@ -27,7 +27,7 @@ from lldbsuite.test import lldbutil
 #  [5] = e\0\0\0
 #}
 
-class Rdar12991846TestCase(TestBase):
+class UnicodeLiteralsTestCase(TestBase):
 
     mydir = TestBase.compute_mydir(__file__)