Remove use of size_t in Rust code

Needed to upgrade bindgen from 0.59.0 to 0.63.0. Resolves the
following errors:

//#[path = "../../../src/options.rs"]
//mod options;

error[E0432]: unresolved import `keystore2_apc_compat_bindgen::size_t`
  --> system/security/keystore2/apc_compat/apc_compat.rs:22:82
   |
22 |     abortUserConfirmation, closeUserConfirmationService, promptUserConfirmation, size_t,
   |
      ^^^^^^ no `size_t` in the root

error[E0412]: cannot find type `size_t` in this scope
  --> system/security/keystore2/apc_compat/apc_compat.rs:79:23
   |
79 |     tbs_message_size: size_t,
   |                       ^^^^^^ not found in this scope

error[E0412]: cannot find type `size_t` in this scope
  --> system/security/keystore2/apc_compat/apc_compat.rs:81:30
   |
81 |     confirmation_token_size: size_t,
   |                              ^^^^^^ not found in this scope

error[E0412]: cannot find type `size_t` in this scope
   --> system/security/keystore2/apc_compat/apc_compat.rs:181:37
    |
181 |                 extra_data.len() as size_t,
    |                                     ^^^^^^ not found in this scope

Test: Treehugger
Change-Id: I848f481627f3c14caa6252eee6b5dd40d2f58eed
diff --git a/keystore2/apc_compat/apc_compat.rs b/keystore2/apc_compat/apc_compat.rs
index 57f8710..9f44927 100644
--- a/keystore2/apc_compat/apc_compat.rs
+++ b/keystore2/apc_compat/apc_compat.rs
@@ -19,7 +19,7 @@
 //! client.
 
 use keystore2_apc_compat_bindgen::{
-    abortUserConfirmation, closeUserConfirmationService, promptUserConfirmation, size_t,
+    abortUserConfirmation, closeUserConfirmationService, promptUserConfirmation,
     tryGetUserConfirmationService, ApcCompatCallback, ApcCompatServiceHandle,
 };
 pub use keystore2_apc_compat_bindgen::{
@@ -76,9 +76,9 @@
     handle: *mut ::std::os::raw::c_void,
     rc: u32,
     tbs_message: *const u8,
-    tbs_message_size: size_t,
+    tbs_message_size: usize,
     confirmation_token: *const u8,
-    confirmation_token_size: size_t,
+    confirmation_token_size: usize,
 ) {
     // # Safety:
     // The C/C++ implementation must pass to us the handle that was created
@@ -178,7 +178,7 @@
                 cb,
                 prompt_text.as_ptr(),
                 extra_data.as_ptr(),
-                extra_data.len() as size_t,
+                extra_data.len() as usize,
                 locale.as_ptr(),
                 ui_opts,
             )