Delete old x86 validator.

src/trusted/validator/x86/ncval_seg_sfi/README

-This directory contains the code for the native client verifier (ncv)
-which checks whether binaries adhere to certain control flow
-and instruction set restrictions. It assumes that segment registers
-are used to control memory accesses.
-
-Note: Although the current builds generate 64-bit versions, they do not
-make any sense, since segment registers have little effect in x86-64.
-
-Debugging
----------
-
-Many of the source files contain #define DEBUGGING flags. When
-DEBUGGING is set to 1, additional debugging print messages are
-compiled into the code. Unfortunately, by default, these message
-frequently call routines that are not compiled into corresponding
-executables (such as ncval and ncdis). To add the additional routines,
-edit file
-
-   native_client/site_scons/site_tools/library_deps.py
-
-For x86-32, edit lines
-
-            # When turning on the DEBUGGING flag in the x86-32 validator
-            # or decoder, add the following:
-            #'nc_opcode_modeling_verbose_x86_32',
-
-to
-
-            # When turning on the DEBUGGING flag in the x86-32 validator
-            # or decoder, add the following:
-            'nc_opcode_modeling_verbose_x86_32',
-
-For x86-64, edit lines
-
-            # When turning on the DEBUGGING flag in the x86-64 validator
-            # or decoder, add the following:
-            # 'nc_opcode_modeling_verbose_x86_64',
-
-to
-
-            # When turning on the DEBUGGING flag in the x86-64 validator
-            # or decoder, add the following:
-            'nc_opcode_modeling_verbose_x86_64',
-
-These changes will make sure that the corresponding print routines are
-added to the executables during link time.