Fix accidental FileCheck variable captures.

These should be simple substitutions rather than captures, so that we're
actually testing the capture from the previous line.

Noticed by inspection.

Author: rudkx

test/SILPasses/constant_propagation.sil

@@ -38,7 +38,7 @@ bb0:
 // CHECK-NOT: integer_literal $Builtin.Int64, 0
 // CHECK-NOT: builtin
 // CHECK: [[RES:%.*]] = integer_literal $Builtin.Int64, 7
-// CHECK-NEXT: return [[RES:%.*]] : $Builtin.Int64
+// CHECK-NEXT: return [[RES]] : $Builtin.Int64
 }
 
 // Fold casts. (This test assumes that DCE does not run, otherwise the unreachable blocks will get removed.)

test/SILPasses/sil_simplify_instrs.sil

@@ -56,7 +56,7 @@ bb0(%x : $Builtin.Int64):
 // CHECK-LABEL: sil @fold_mul_with_overflow_zeros
 // CHECK-NOT: builtin "int_smul_with_overflow_Int64"
 // CHECK: [[RES:%.*]] = integer_literal $Builtin.Int64, 0
-// CHECK-NEXT: return [[RES:%.*]] : $Builtin.Int64
+// CHECK-NEXT: return [[RES]] : $Builtin.Int64
 }
 
 // Simplify arithmetic where one operand is a one and the other is not a constant