Remove unnecessary calling of PayloadGenerator

PayloadGenerator object is created twice, introduced in:
1f93ce20c5a5f3e7c2f6b5e1f9fdc4d2572220cc

Remove this extra call.

Test: atest --host releasetools_test
Change-Id: I7701542f7f53c9295a44fc23f634d863ab4cfc52
diff --git a/tools/releasetools/merge_ota.py b/tools/releasetools/merge_ota.py
index 24d9ea9..fb5957a 100644
--- a/tools/releasetools/merge_ota.py
+++ b/tools/releasetools/merge_ota.py
@@ -243,8 +243,6 @@
   # Get signing keys
   key_passwords = common.GetKeyPasswords([args.package_key])
 
-  generator = PayloadGenerator()
-
   apex_info_bytes = ApexInfo(file_paths)
 
   with tempfile.NamedTemporaryFile() as unsigned_payload: