Remove ab_update=true from dynamic_partition_list.txt

When building with Make, this entry is present only in misc_info.txt and
not not in dynamic_partition_list.txt. This entry gets added to the
first file via `dump-super-image-info`.

This CL ports this behavior to Soong by moving this entry out of
`dumpDynamicPartitionInfo` and into `buildMiscInfo`

Bug: 399788100
Test: Verified that this entry is present in Soong's misc_info.txt
Test: Verified that this entry is absent in Soong's
dynamic_partition_info.txt

Change-Id: I98384510c7f47c403ca5d7edbf863e513c9d503d
diff --git a/filesystem/super_image.go b/filesystem/super_image.go
index 9e4412c..5108025 100644
--- a/filesystem/super_image.go
+++ b/filesystem/super_image.go
@@ -200,6 +200,7 @@
 		miscInfoString.WriteString(value)
 		miscInfoString.WriteRune('\n')
 	}
+	addStr("ab_update", strconv.FormatBool(proptools.Bool(s.properties.Ab_update)))
 
 	subImageInfo := make(map[string]FilesystemInfo)
 	var deps android.Paths
@@ -329,8 +330,6 @@
 	addStr("super_partition_groups", strings.Join(groups, " "))
 	addStr("dynamic_partition_list", strings.Join(partitionList, " "))
 
-	addStr("ab_update", strconv.FormatBool(proptools.Bool(s.properties.Ab_update)))
-
 	if proptools.Bool(s.properties.Virtual_ab.Enable) {
 		addStr("virtual_ab", "true")
 		if proptools.Bool(s.properties.Virtual_ab.Retrofit) {