message: remove all checks for gdal 2.0
diff: @@ -3,10 +3,8 @@ use crate::vector::geometry::Geometry;
  use crate::vector::layer::Layer;
  use crate::vector::Defn;
  use gdal_sys::{self, OGRErr, OGRFeatureH, OGRFieldType};
  -#[cfg(major_ge_2)]
  use libc::c_longlong;
  use libc::{c_double, c_int};
  -#[cfg(major_ge_2)]
  use std::convert::TryInto;
  use std::ffi::CString;
  @@ -78,7 +76,6 @@ impl<'a> Feature<'a> {
  let rv = unsafe { gdal_sys::OGR_F_GetFieldAsInteger(self.c_feature, field_id) };
  Ok(FieldValue::IntegerValue(rv as i32))
  }
  - #[cfg(major_ge_2)]
  OGRFieldType::OFTInteger64 => {
  let rv = unsafe { gdal_sys::OGR_F_GetFieldAsInteger64(self.c_feature, field_id) };
  Ok(FieldValue::Integer64Value(rv))
  @@ -234,7 +231,6 @@ impl<'a> Feature<'a> {
  Ok(())
  }
  - #[cfg(major_ge_2)]
  pub fn set_field_integer64(&self, field_name: &str, value: i64) -> Result<()> {
  let c_str_field_name = CString::new(field_name)?;
  let idx =
  @@ -294,8 +290,6 @@ impl<'a> Feature<'a> {
  FieldValue::RealValue(value) => self.set_field_double(field_name, value),
  FieldValue::StringValue(ref value) => self.set_field_string(field_name, value.as_str()),
  FieldValue::IntegerValue(value) => self.set_field_integer(field_name, value),
  -
  - #[cfg(major_ge_2)]
  FieldValue::Integer64Value(value) => self.set_field_integer64(field_name, value),
  #[cfg(feature = "datetime")]
  @@ -331,7 +325,6 @@ impl<'a> Drop for Feature<'a> {
  pub enum FieldValue {
  IntegerValue(i32),
  - #[cfg(major_ge_2)]
  Integer64Value(i64),
  StringValue(String),
  RealValue(f64),
  @@ -364,14 +357,12 @@ impl FieldValue {
  pub fn into_int(self) -> Option<i32> {
  match self {
  FieldValue::IntegerValue(rv) => Some(rv),
  - #[cfg(major_ge_2)]
  FieldValue::Integer64Value(rv) => rv.try_into().ok(),
  _ => None,
  }
  }
  /// Interpret the value as `i64`. Returns `None` if the value is something else.
  - #[cfg(major_ge_2)]
  pub fn into_int64(self) -> Option<i64> {
  match self {
  FieldValue::IntegerValue(rv) => Some(rv as i64),
  