[MC][MIPS] Remove unused check prefixes

Author: RKSimon

llvm/test/MC/Mips/mips-expansions-bad.s

@@ -1,9 +1,9 @@
 # RUN: not llvm-mc %s -arch=mips -mcpu=mips32r2 2>%t1
 # RUN: FileCheck %s < %t1 --check-prefix=32-BIT
 # RUN: not llvm-mc %s -arch=mips64 -mcpu=mips64 -target-abi n32 2>&1 | \
-# RUN:   FileCheck %s --check-prefixes=64-BIT,N32-ONLY
+# RUN:   FileCheck %s --check-prefix=64-BIT
 # RUN: not llvm-mc %s -arch=mips64 -mcpu=mips64 -target-abi n64 2>&1 | \
-# RUN:   FileCheck %s --check-prefixes=64-BIT,N64-ONLY
+# RUN:   FileCheck %s --check-prefix=64-BIT
 
   .text
   dli $5, 1