aya-bpf-cty: remove empty module

This triggers the unused import lint after
https://github.com/rust-lang/rust/commit/482275b19422b871b986ec0400257a.

bpf/aya-bpf-cty/src/lib.rs

@@ -12,8 +12,6 @@
 pub use ad::*;
 // OD = OS dependent
 pub use od::*;
-// PWD = Pointer Width Dependent
-pub use pwd::*;
 
 #[cfg(target_arch = "bpf")]
 mod ad {
@@ -106,12 +104,6 @@ mod od {
     pub type c_ulong = u64;
 }
 
-#[cfg(target_pointer_width = "32")]
-mod pwd {}
-
-#[cfg(target_pointer_width = "64")]
-mod pwd {}
-
 pub type int8_t = i8;
 pub type int16_t = i16;
 pub type int32_t = i32;