sign_target_files_apks: replacing GKI signing args completely

Commit I8bd8ad3acf324931b47d45fd30bc590206b1927e adds a default
value of "gki_signing_signature_args" in the misc_info.txt for
release signing to work. However, it's better to replace the default
value entirely (e.g., --prop foo:bar) as there is no need to include
them in the final release-signed image.

Bug: 178559811
Bug: 177862434
Test: atest releasetools_test
Test: atest releasetools_py3_test
Change-Id: I060b5a7076ff3e5d883abeb7d72f3db887c9fd69
diff --git a/tools/releasetools/sign_target_files_apks.py b/tools/releasetools/sign_target_files_apks.py
index 313d1e6..0281e27 100755
--- a/tools/releasetools/sign_target_files_apks.py
+++ b/tools/releasetools/sign_target_files_apks.py
@@ -1029,9 +1029,8 @@
 
   extra_args = OPTIONS.gki_signing_extra_args
   if extra_args:
-    print('Setting extra GKI signing args: "%s"' % (extra_args))
-    misc_info["gki_signing_signature_args"] = (
-        misc_info.get("gki_signing_signature_args", '') + ' ' + extra_args)
+    print('Setting GKI signing args: "%s"' % (extra_args))
+    misc_info["gki_signing_signature_args"] = extra_args
 
 
 def BuildKeyMap(misc_info, key_mapping_options):