[NFC][InstCombine] Update few comment updates i missed in 0ac56e8eaa

As pointed out in post-commit review in that commit

llvm/test/Transforms/InstCombine/apint-shift.ll

@@ -209,8 +209,6 @@ define <2 x i7> @shl_lshr_splat_vec(<2 x i7> %X) {
   ret <2 x i7> %sh2
 }
 
-; Don't hide the shl from scalar evolution. DAGCombine will get it.
-
 define i23 @test11(i23 %x) {
 ; CHECK-LABEL: @test11(
 ; CHECK-NEXT:    [[TMP1:%.*]] = mul i23 [[X:%.*]], 6
@@ -245,8 +243,6 @@ define <2 x i47> @test12_splat_vec(<2 x i47> %X) {
   ret <2 x i47> %sh2
 }
 
-; Don't hide the shl from scalar evolution. DAGCombine will get it.
-
 define i18 @test13(i18 %x) {
 ; CHECK-LABEL: @test13(
 ; CHECK-NEXT:    [[TMP1:%.*]] = mul i18 [[X:%.*]], 6

llvm/test/Transforms/InstCombine/cast.ll

@@ -694,7 +694,6 @@ define i64 @test50(i64 %x) {
   %D = add i32 %B, -1
   %E = sext i32 %D to i64
   ret i64 %E
-; lshr+shl will be handled by DAGCombine.
 }
 
 define i64 @test51(i64 %A, i1 %cond) {

llvm/test/Transforms/InstCombine/shift.ll

@@ -82,9 +82,7 @@ define i8 @test10a(i8 %A) {
   ret i8 %C
 }
 
-;; This transformation is deferred to DAGCombine:
 ;; (A >> 3) << 4 === (A & 0x1F) << 1
-;; The shl may be valuable to scalar evolution.
 define i8 @test11(i8 %x) {
 ; CHECK-LABEL: @test11(
 ; CHECK-NEXT:    [[TMP1:%.*]] = mul i8 [[X:%.*]], 6
@@ -109,7 +107,6 @@ define i8 @test11a(i8 %A) {
   ret i8 %C
 }
 
-;; This is deferred to DAGCombine unless %B is single-use.
 ;; (A >> 8) << 8 === A & -256
 define i32 @test12(i32 %A) {
 ; CHECK-LABEL: @test12(
@@ -137,9 +134,7 @@ define i8 @shishi(i8 %x) {
   ret i8 %r
 }
 
-;; This transformation is deferred to DAGCombine:
 ;; (A >> 3) << 4 === (A & -8) * 2
-;; The shl may be valuable to scalar evolution.
 define i8 @test13(i8 %x) {
 ; CHECK-LABEL: @test13(
 ; CHECK-NEXT:    [[TMP1:%.*]] = mul i8 [[X:%.*]], 6