[clang-format] Fix test failure caused by "rm" on some buildbots.

The begining command "rm" will return 1 when there is not such file to
delete.

This patch is to remove it, as it's not needed for the test.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@296453 91177308-0d34-0410-b5e6-96231b3b80d8

test/Format/inplace.cpp

 // Regression test to check that clang-format does not leave behind temporary
 // files on Windows when doing in-place formatting.
-// RUN: rm %T/inplace*
 // RUN: cp %s %T/inplace.cpp
 // RUN: clang-format -style=LLVM -i %T/inplace.cpp
 // RUN: ls %T > %T/files.txt