Delete old x86 validator.

src/trusted/validator/x86/testing/enuminsts/README_scons.txt

-Copyright (c) 2012 The Native Client Authors. All rights reserved.
-Use of this source code is governed by a BSD-style license that be
-found in the LICENSE file.
-
-************************************************************************
- NOTE: The Scons version of enuminst is documented in this file.
- It has less functionality than the Makefile version.
-************************************************************************
-
-Exhaustive instruction enumeration test for x86 Native Client decoder.
-Limited testing of validator.
-
-SCONS now builds the 32- and 64-bit versions of enuminst. The scons
-build incorporates NaCl and Ragel-Deterministic Finite Automata (R-DFA)
-validators. It does not include Xed.
-
-The binaries are available in (for example)
-    scons-out/opt-linux-x86-64/staging/enuminst
-    scons-out/opt-linux-x86-32/staging/enuminst
-
-Some suggestions on running enuminst:
-  enuminst --legalnacl --legal=nacl --legal=ragel
-    Compare lengths of instructions that decode for nacl.
-    Filters out most NaCl illegal instructions.
-
-  enuminst --illegal=nacl --legal=ragel --print=ragel
-    Identifies instructions legal for R-DFA but not nacl.
-
-  enuminst --nacllegal --legal=nacl --illegal=ragel --print=nacl
-    Identifies instructions legal for nacl but not R-DFA.
-
-The NaCl validator supports a partial-validation mode, which for a
-a single instruction determines if it could or could not appear in
-a legal Native Client module. Instructions such as "ret" can never
-appear in a valid NaCl module, and are rejected. Instructions such
-as "jmp *%eax" can appear, so  they are accepted.