avcodec: revert some changes that weren't pertintent to 2.8

Author: meh

Diff for: src/avcodec/codec.rs

@@ -670,9 +670,6 @@ pub struct AVPacket {
 	pub flags: c_int,
 	pub side_data: *mut AVPacketSideData,
 	pub side_data_elems: c_int,
-	#[cfg(feature = "ff_api_convergence_duration_is_defined")] // see FFmpeg commit b01891a9 (no other way to distinguish size of duration field)
-	pub duration: int64_t,
-	#[cfg(not(feature = "ff_api_convergence_duration_is_defined"))]
 	pub duration: c_int,
 	#[cfg(feature = "ff_api_destruct_packet")]
 	pub destruct: Option<extern fn(*mut AVPacket)>,
@@ -935,7 +932,7 @@ pub struct AVCodecContext {
 	pub priv_data: *mut c_void,
 	pub internal: *mut AVCodecInternal,
 	pub opaque: *mut c_void,
-	pub bit_rate: int64_t,
+	pub bit_rate: c_int,
 	pub bit_rate_tolerance: c_int,
 	pub global_quality: c_int,
 	pub compression_level: c_int,