revert avro timestamp-millis mapping (apache#2223)

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# Rationale for this change
Follow up to apache#2173, the conversion as implemented is not safe since
iceberg does not natively have `millis` precision. Timestamp values are
implicitly in `micros` precision
This is confirmed by
apache#2173 (comment)

Let's revert for now and follow up to figure out the right way to
support `millis` precision.

# Are these changes tested?

# Are there any user-facing changes?

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Author: kevinjqliu

pyiceberg/utils/schema_conversion.py

@@ -69,7 +69,6 @@
 LOGICAL_FIELD_TYPE_MAPPING: Dict[Tuple[str, str], PrimitiveType] = {
     ("date", "int"): DateType(),
     ("time-micros", "long"): TimeType(),
-    ("timestamp-millis", "int"): TimestampType(),
     ("timestamp-micros", "long"): TimestampType(),
     ("uuid", "fixed"): UUIDType(),
     ("uuid", "string"): UUIDType(),

tests/utils/test_schema_conversion.py

@@ -341,12 +341,6 @@ def test_convert_uuid_fixed_type() -> None:
     assert actual == UUIDType()
 
 
-def test_convert_timestamp_millis_type() -> None:
-    avro_logical_type = {"type": "int", "logicalType": "timestamp-millis"}
-    actual = AvroSchemaConversion()._convert_logical_type(avro_logical_type)
-    assert actual == TimestampType()
-
-
 def test_convert_timestamp_micros_type() -> None:
     avro_logical_type = {"type": "int", "logicalType": "timestamp-micros"}
     actual = AvroSchemaConversion()._convert_logical_type(avro_logical_type)