Set entryCost to zero on TechHidden parts (#920)

A TechHidden part's entryCost isn't included in the price shown on the
tech node's "purchase all parts" button, but clicking the button
actually charges the player for hidden parts nonetheless.  This is a bug
in the game, but it has a simple workaround: set entryCost to zero on
parts that have the TechHidden flag.  (Squad's deprecated parts do this
too.)

Distribution/RestockPlus/GameData/ReStockPlus/Parts/Aero/1875/restock-nosecone-1875-1.cfg

@@ -18,7 +18,7 @@ PART
   node_stack_bottom = 0.0, -0.94, 0, 0.0, -1.0, 0.0, 1
   // Tech
   TechRequired = aerodynamicSystems
-  entryCost = 4200
+  entryCost = 0
   // Info
   cost = 480
   category = none

Distribution/RestockPlus/GameData/ReStockPlus/Parts/Coupling/0625/restock-claw-625-1.cfg

@@ -17,7 +17,7 @@ PART
   node_attach = 0.0, -0.01, 0.0, 0.0, -1.0, 0.0, 0
   node_stack_bottom = 0.0, -0.06, 0.0, 0.0, -1.0, 0.0, 0
   TechRequired = actuators
-  entryCost = 4000
+  entryCost = 0
   cost = 350
   mass = 0.03
   category = none

Distribution/RestockPlus/GameData/ReStockPlus/Patches/MakingHistoryPartHiding.cfg

@@ -3,6 +3,7 @@
 @PART[*]:HAS[#MHReplacement[True]]:FOR[zzReStockPlus]:NEEDS[SquadExpansion/MakingHistory]
 {
   %TechHidden = True
+  @entryCost = 0
   @category = none
   @subcategory = 0
   !MODULE[ModuleTestSubject] {}