avbctl: Remove comment and code about ro.boot.slot.

The presence of this comment and code is confusing as only
ro.boot.slot_suffix is used and this will always have a leading
underscore. Remove it.

Bug: 37663204
Test: All unit tests pass.
Change-Id: I824626c0c6d8b7ed2b19cca495c533a6e202fa24

tools/avbctl/avbctl.cc

@@ -220,21 +220,9 @@ int do_get_verity(AvbOps* ops, const std::string& ab_suffix) {
 /* Helper function to get A/B suffix, if any. If the device isn't
  * using A/B the empty string is returned. Otherwise either "_a",
  * "_b", ... is returned.
- *
- * Note that since sometime in O androidboot.slot_suffix is deprecated
- * and androidboot.slot should be used instead. Since bootloaders may
- * be out of sync with the OS, we check both and for extra safety
- * prepend a leading underscore if there isn't one already.
  */
 std::string get_ab_suffix() {
-  std::string ab_suffix = android::base::GetProperty("ro.boot.slot_suffix", "");
-  if (ab_suffix == "") {
-    ab_suffix = android::base::GetProperty("ro.boot.slot", "");
-  }
-  if (ab_suffix.size() > 0 && ab_suffix[0] != '_') {
-    ab_suffix = std::string("_") + ab_suffix;
-  }
-  return ab_suffix;
+  return android::base::GetProperty("ro.boot.slot_suffix", "");
 }
 
 }  // namespace