Revert "[AArch64] Select SMULL for zero extended vectors when top bit is zero"

This reverts commit f9e03907.

The patch causes a crash for the IR below:

target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
target triple = "arm64-apple-macosx"

define void @test(ptr %data, <8 x i16> %v) {
entry:
  %0 = sext <8 x i16> %v to <8 x i32>
  %1 = mul <8 x i32> %0, <i32 35584, i32 35584, i32 35584, i32 35584, i32 35584, i32 35584, i32 35584, i32 35584>
  %2 = lshr <8 x i32> %1, <i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1>
  %3 = trunc <8 x i32> %2 to <8 x i16>
  store <8 x i16> %3, ptr %data, align 2
  ret void
}