Update CustomInputType functions comment

Update CustomInputType functions comment to reflect that they are now optional and OEMs are free to use any int32 to represent an custom input event.

Bug: 255390449
Test: m (built)
Change-Id: I8878c1330f7fe3ba35ea10307a4ba4c4c88b1d57
diff --git a/current.txt b/current.txt
index afde7b1..146ded6 100644
--- a/current.txt
+++ b/current.txt
@@ -929,4 +929,7 @@
 1bac6a7c8136dfb0414fe5639eec115aa2d12927e64a0642a43fb53225f099b2 android.hardware.wifi@1.6::IWifiStaIface
 0a800e010e8eb6eecdfdc96f04fd2ae2f417a79a74a7c0eec3a9f539199bccd4 android.hardware.wifi@1.6::types
 
+# ABI preserving changes to HALs during Android U
+2aa559cda86c358c6429114ef6bc72c1b43281e98f9eb6b4df5e7073c8d05767 android.hardware.automotive.vehicle@2.0::types
+
 # There will be no more HIDL HALs. Use AIDL instead.