cmake: Remove ENABLE_X86_SHANI from bitcoin-build-config.h

`ENABLE_X86_SHANI` is already conditionally defined for the
`bitcoin_crypto` target, so defining it in `bitcoin-build-config.h` is
redundant.

cmake/bitcoin-build-config.h.in

@@ -42,9 +42,6 @@
 /* Define to 1 to enable wallet functions. */
 #cmakedefine ENABLE_WALLET 1
 
-/* Define this symbol to build code that uses x86 SHA-NI intrinsics */
-#cmakedefine ENABLE_X86_SHANI 1
-
 /* Define to 1 if you have the declaration of `fork', and to 0 if you don't.
    */
 #cmakedefine01 HAVE_DECL_FORK

cmake/introspection.cmake

@@ -200,7 +200,6 @@ if(NOT MSVC)
     " HAVE_X86_SHANI
     CXXFLAGS ${X86_SHANI_CXXFLAGS}
   )
-  set(ENABLE_X86_SHANI ${HAVE_X86_SHANI})
 
   # Check for ARMv8 SHA-NI intrinsics.
   set(ARM_SHANI_CXXFLAGS -march=armv8-a+crypto)