[JumpThreading] Rename thread-prob-3.ll to thread-prob-1.ll (NFC)

I just removed thread-prob-{1,2}.ll in
b2f05fae80b0c1a307a9e257157a0d70e6623eb8, so I am removing
thread-prob-3.ll to thread-prob-1.ll.

diff --git a/llvm/test/Transforms/JumpThreading/thread-prob-3.ll b/llvm/test/Transforms/JumpThreading/thread-prob-1.ll
similarity index 100%
rename from llvm/test/Transforms/JumpThreading/thread-prob-3.ll
rename to llvm/test/Transforms/JumpThreading/thread-prob-1.ll