Revert "glasm: Skip phi moves on undefined instructions"

Causes regressions on Bowser's Fury.

src/shader_recompiler/backend/glasm/emit_glasm_not_implemented.cpp

@@ -58,9 +58,7 @@ void EmitPhiMove(EmitContext& ctx, const IR::Value& phi_value, const IR::Value&
     }
     const Register phi_reg{ctx.reg_alloc.Consume(IR::Value{&phi})};
     const Value eval_value{ctx.reg_alloc.Consume(value)};
-    if (!value.IsImmediate() && IR::IsUndef(RegAlloc::AliasInst(*value.Inst()))) {
-        return;
-    }
+
     if (phi_reg == eval_value) {
         return;
     }

src/shader_recompiler/frontend/ir/value.h

@@ -395,17 +395,4 @@ inline f64 Value::F64() const {
     return inst.GetOpcode() == Opcode::Phi;
 }
 
-[[nodiscard]] inline bool IsUndef(const Inst& inst) {
-    switch (inst.GetOpcode()) {
-    case Opcode::UndefU1:
-    case Opcode::UndefU8:
-    case Opcode::UndefU16:
-    case Opcode::UndefU32:
-    case Opcode::UndefU64:
-        return true;
-    default:
-        return false;
-    }
-}
-
 } // namespace Shader::IR