clippy: Remove unused import

[brooksprumo]

Problem

There are nightly clippy warnings that will prevent upgrading our stable Rust version.

For this PR, it's this one:

warning: unused import: `target_arch::*`
 --> zk-token-sdk/src/zk_token_elgamal/convert.rs:1:9
  |
1 | pub use target_arch::*;
  |         ^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

Summary of Changes

Removes unused import.

[codecov]

Codecov Report

Merging #34050 (a6f5f56) into master (47a98eb) will decrease coverage by 0.1%.
Report is 3 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #34050     +/-   ##
=========================================
- Coverage    81.9%    81.9%   -0.1%     
=========================================
  Files         811      811             
  Lines      219552   219552             
=========================================
- Hits       179902   179851     -51     
- Misses      39650    39701     +51     

[samkim-crypto]

Looks fine to me. Thanks!