Remove length modifier when using assignment suppression in TimerTest

Summary:
This is useless and it's giving warnings in the build bots:
/home/motus/netbsd8/netbsd8/llvm/tools/lldb/unittests/Utility/TimerTest.cpp:67:43: warning: use of assignment suppression and length modifier together in gnu_scanf format [-Wformat=]

Reviewers: xiaobai

Subscribers: krytarowski, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D62626

llvm-svn: 362107