Remove mount_point property from system images

This causes another layer of system/ folders in the built image,
which differs from make.

Bug: 381120092
Test: diff'd mounted images
Change-Id: I938178bf2358cf90cea1e8f3f5a06a3de7096b84
diff --git a/fsgen/filesystem_creator.go b/fsgen/filesystem_creator.go
index 4e1ca9e..35d2e44 100644
--- a/fsgen/filesystem_creator.go
+++ b/fsgen/filesystem_creator.go
@@ -763,8 +763,9 @@
 	}
 
 	fsProps.Is_auto_generated = proptools.BoolPtr(true)
-	// TODO(b/381120092): Verify mount_point for system partition
-	fsProps.Mount_point = proptools.StringPtr(partitionType)
+	if partitionType != "system" {
+		fsProps.Mount_point = proptools.StringPtr(partitionType)
+	}
 
 	partitionSpecificFsProps(ctx, fsProps, partitionVars, partitionType)