Remove unreachable x64 lowerings for iadd_imm (bytecodealliance#4726)

All of the `*_imm` instructions are rewritten during legalization to an
explicit `iconst` plus the general form of the operator, so backends
never see them. Therefore these ISLE rules in the x64 backend can never
match anything.

cranelift/codegen/src/isa/x64/lower.isle

@@ -189,37 +189,6 @@
 
 ;; (No `iadd_ifcout` for `i128`.)
 
-;;;; Rules for `iadd_imm` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
-;; `i64` and smaller.
-
-;; When the immediate fits in a `RegMemImm.Imm`, use that.
-(rule (lower (has_type (fits_in_64 ty) (iadd_imm y (simm32_from_imm64 x))))
-      (x64_add ty y x))
-
-;; Otherwise, put the immediate into a register.
-(rule (lower (has_type (fits_in_64 ty) (iadd_imm y (u64_from_imm64 x))))
-      (x64_add ty y (imm ty x)))
-
-;; `i128`
-
-;; When the immediate fits in a `RegMemImm.Imm`, use that.
-(rule (lower (has_type $I128 (iadd_imm y (simm32_from_imm64 x))))
-      (let ((y_regs ValueRegs y)
-            (y_lo Gpr (value_regs_get_gpr y_regs 0))
-            (y_hi Gpr (value_regs_get_gpr y_regs 1)))
-        (with_flags (x64_add_with_flags_paired $I64 y_lo x)
-                    (x64_adc_paired $I64 y_hi (RegMemImm.Imm 0)))))
-
-;; Otherwise, put the immediate into a register.
-(rule (lower (has_type $I128 (iadd_imm y (u64_from_imm64 x))))
-      (let ((y_regs ValueRegs y)
-            (y_lo Gpr (value_regs_get_gpr y_regs 0))
-            (y_hi Gpr (value_regs_get_gpr y_regs 1))
-            (x_lo Gpr (imm $I64 x)))
-        (with_flags (x64_add_with_flags_paired $I64 y_lo x_lo)
-                    (x64_adc_paired $I64 y_hi (RegMemImm.Imm 0)))))
-
 ;;;; Rules for `isub` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 ;; `i64` and smaller.