ObsoleteFiles.inc: Add an entry for libdtrace.so.2 in /usr/lib

There was a window between commits 4ae699122810 ("dtrace: Add
WITH_DTRACE_ASAN") and 848ff9bc1b97 ("libdtrace: Explicitly set SHLIBDIR
and SHLIB_MAJOR") where libdtrace.so.2 was being installed to /usr/lib
instead of /lib.