[PhaseOrdering] Remove unused check-prefixes

Just use default CHECK in most cases.
diff --git a/llvm/test/Transforms/PhaseOrdering/inlining-alignment-assumptions.ll b/llvm/test/Transforms/PhaseOrdering/inlining-alignment-assumptions.ll
index 2605701..59243a9 100644
--- a/llvm/test/Transforms/PhaseOrdering/inlining-alignment-assumptions.ll
+++ b/llvm/test/Transforms/PhaseOrdering/inlining-alignment-assumptions.ll
@@ -1,7 +1,7 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -S -O2 -preserve-alignment-assumptions-during-inlining=0 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-OFF,FALLBACK-0
-; RUN: opt -S -O2 -preserve-alignment-assumptions-during-inlining=1 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-ON,FALLBACK-1
-; RUN: opt -S -O2 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-OFF,FALLBACK-DEFAULT
+; RUN: opt -S -O2 -preserve-alignment-assumptions-during-inlining=0 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-OFF
+; RUN: opt -S -O2 -preserve-alignment-assumptions-during-inlining=1 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-ON
+; RUN: opt -S -O2 < %s | FileCheck %s --check-prefixes=CHECK,ASSUMPTIONS-OFF
 
 target datalayout = "e-p:64:64-p5:32:32-A5"