Remove duplicate typedef. (#3975)

php/ext/google/protobuf/protobuf.h

@@ -608,48 +608,36 @@ typedef struct Api Api;
 typedef struct BoolValue BoolValue;
 typedef struct BytesValue BytesValue;
 typedef struct Descriptor Descriptor;
-typedef struct Descriptor Descriptor;
 typedef struct DescriptorPool DescriptorPool;
 typedef struct DoubleValue DoubleValue;
 typedef struct Duration Duration;
-typedef struct Enum Enum;
 typedef struct EnumDescriptor EnumDescriptor;
-typedef struct EnumDescriptor EnumDescriptor;
-typedef struct EnumValue EnumValue;
-typedef struct EnumValueDescriptor EnumValueDescriptor;
+typedef struct Enum Enum;
 typedef struct EnumValueDescriptor EnumValueDescriptor;
-typedef struct Field Field;
-typedef struct FieldDescriptor FieldDescriptor;
-typedef struct FieldDescriptor FieldDescriptor;
-typedef struct FieldMask FieldMask;
+typedef struct EnumValue EnumValue;
 typedef struct Field_Cardinality Field_Cardinality;
+typedef struct FieldDescriptor FieldDescriptor;
+typedef struct Field Field;
 typedef struct Field_Kind Field_Kind;
+typedef struct FieldMask FieldMask;
 typedef struct FloatValue FloatValue;
 typedef struct GPBEmpty GPBEmpty;
 typedef struct Int32Value Int32Value;
 typedef struct Int64Value Int64Value;
 typedef struct InternalDescriptorPool InternalDescriptorPool;
 typedef struct ListValue ListValue;
-typedef struct Map Map;
-typedef struct Map Map;
-typedef struct MapIter MapIter;
 typedef struct MapIter MapIter;
+typedef struct Map Map;
 typedef struct MessageField MessageField;
-typedef struct MessageField MessageField;
-typedef struct MessageHeader MessageHeader;
 typedef struct MessageHeader MessageHeader;
 typedef struct MessageLayout MessageLayout;
-typedef struct MessageLayout MessageLayout;
 typedef struct Method Method;
 typedef struct Mixin Mixin;
 typedef struct NullValue NullValue;
 typedef struct Oneof Oneof;
-typedef struct Oneof Oneof;
 typedef struct Option Option;
-typedef struct RepeatedField RepeatedField;
-typedef struct RepeatedField RepeatedField;
-typedef struct RepeatedFieldIter RepeatedFieldIter;
 typedef struct RepeatedFieldIter RepeatedFieldIter;
+typedef struct RepeatedField RepeatedField;
 typedef struct SourceContext SourceContext;
 typedef struct StringValue StringValue;
 typedef struct Struct Struct;