Revert "[ARM] Add ARMv8-M security extension instructions to ARMv8-M Baseline/Mainline"

This reverts commit r257883.

Somehow this didn't make it into r257916.

llvm-svn: 257919
diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 277304d..5a63f04 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -5268,7 +5268,7 @@
       Mnemonic == "vcvta" || Mnemonic == "vcvtn"  || Mnemonic == "vcvtp" ||
       Mnemonic == "vcvtm" || Mnemonic == "vrinta" || Mnemonic == "vrintn" ||
       Mnemonic == "vrintp" || Mnemonic == "vrintm" || Mnemonic == "hvc" ||
-      Mnemonic == "bxns"  || Mnemonic == "blxns" || Mnemonic.startswith("vsel"))
+      Mnemonic.startswith("vsel"))
     return Mnemonic;
 
   // First, split out any predication code. Ignore mnemonics we know aren't