init: degeneralize subcontext init into only vendor_init

This code is more generic than it needs to be and one of the side
effects is that an extra init process is forked for odm_init, despite
it having the same context as vendor_init.  I don't think anything is
going to change regarding that soon, so this change stops forking that
extra process to save its memory and simplifies the code overall.

Bug: 141164879
Test: init still uses vendor_init for vendor_scripts
Test: init unit tests
Test: init only has one subcontext process
Change-Id: I0d224455604a681711e32f89fb20132378f69060
diff --git a/init/action_parser.h b/init/action_parser.h
index 2fe9983..3000132 100644
--- a/init/action_parser.h
+++ b/init/action_parser.h
@@ -30,8 +30,8 @@
 
 class ActionParser : public SectionParser {
   public:
-    ActionParser(ActionManager* action_manager, std::vector<Subcontext>* subcontexts)
-        : action_manager_(action_manager), subcontexts_(subcontexts), action_(nullptr) {}
+    ActionParser(ActionManager* action_manager, Subcontext* subcontext)
+        : action_manager_(action_manager), subcontext_(subcontext), action_(nullptr) {}
     Result<void> ParseSection(std::vector<std::string>&& args, const std::string& filename,
                               int line) override;
     Result<void> ParseLineSection(std::vector<std::string>&& args, int line) override;
@@ -39,7 +39,7 @@
 
   private:
     ActionManager* action_manager_;
-    std::vector<Subcontext>* subcontexts_;
+    Subcontext* subcontext_;
     std::unique_ptr<Action> action_;
 };