std.Target: Remove Cpu.Arch.spu_2.

This was for a hobby project that appears to be dormant for now. This can be
added back if the project is resumed in the future.

src/codegen/llvm.zig

@@ -98,7 +98,6 @@ pub fn targetTriple(allocator: Allocator, target: std.Target) ![]const u8 {
         .ve => "ve",
 
         .kalimba,
-        .spu_2,
         .propeller1,
         .propeller2,
         => unreachable, // Gated by hasLlvmSupport().
@@ -13024,7 +13023,6 @@ pub fn initializeLLVMTarget(arch: std.Target.Cpu.Arch) void {
 
         // LLVM does does not have a backend for these.
         .kalimba,
-        .spu_2,
         .propeller1,
         .propeller2,
         => unreachable,