Use tableDict for DeltaValue lookbacks

Was abusing the set/getCount machinery before.
diff --git a/Lib/fontTools/ttLib/tables/otBase.py b/Lib/fontTools/ttLib/tables/otBase.py
index 5191ec3..5745fe1 100644
--- a/Lib/fontTools/ttLib/tables/otBase.py
+++ b/Lib/fontTools/ttLib/tables/otBase.py
@@ -574,7 +574,7 @@
 
 			else:
 				table[conv.name] = conv.read(reader, font, table)
-				if conv.isCount or conv.isSize:
+				if conv.isCount:
 					reader.setCount(conv.name, table[conv.name])
 
 		self.postRead(table, font)
@@ -617,8 +617,6 @@
 				writer.writeCountReference(table, conv.name)
 			else:
 				conv.write(writer, font, table, value)
-				if conv.isSize:
-					writer.setCount(conv.name, value)
 	
 	def readFormat(self, reader):
 		pass
diff --git a/Lib/fontTools/ttLib/tables/otConverters.py b/Lib/fontTools/ttLib/tables/otConverters.py
index 765c5fe..1c473ef 100644
--- a/Lib/fontTools/ttLib/tables/otConverters.py
+++ b/Lib/fontTools/ttLib/tables/otConverters.py
@@ -46,7 +46,6 @@
 		self.repeatOffset = repeatOffset
 		self.tableClass = tableClass
 		self.isCount = name.endswith("Count")
-		self.isSize = name.endswith("Size") or name=="DeltaFormat"
 	
 	def read(self, reader, font, tableDict):
 		"""Read a value from the reader."""
@@ -283,9 +282,9 @@
 class DeltaValue(BaseConverter):
 	
 	def read(self, reader, font, tableDict):
-		StartSize = reader.getCount("StartSize")
-		EndSize = reader.getCount("EndSize")
-		DeltaFormat = reader.getCount("DeltaFormat")
+		StartSize = tableDict["StartSize"]
+		EndSize = tableDict["EndSize"]
+		DeltaFormat = tableDict["DeltaFormat"]
 		assert DeltaFormat in (1, 2, 3), "illegal DeltaFormat"
 		nItems = EndSize - StartSize + 1
 		nBits = 1 << DeltaFormat
@@ -306,9 +305,9 @@
 		return DeltaValue
 	
 	def write(self, writer, font, tableDict, value, repeatIndex=None):
-		StartSize = writer.getCount("StartSize")
-		EndSize = writer.getCount("EndSize")
-		DeltaFormat = writer.getCount("DeltaFormat")
+		StartSize = tableDict["StartSize"]
+		EndSize = tableDict["EndSize"]
+		DeltaFormat = tableDict["DeltaFormat"]
 		DeltaValue = value
 		assert DeltaFormat in (1, 2, 3), "illegal DeltaFormat"
 		nItems = EndSize - StartSize + 1