Drop unused `zeroize_derive` feature dependency

[ctz]

This seems to be unused, and has the effect of removing several large proc macro dependencies from the dependency tree:

--- before  2024-07-29 11:07:47.128726312 +0100
+++ after   2024-07-29 11:08:01.911637253 +0100
@@ -24,15 +24,6 @@
 ├── paste v1.0.15 (proc-macro)
 ├── untrusted v0.7.1
 └── zeroize v1.8.1
-    └── zeroize_derive v1.4.2 (proc-macro)
-        ├── proc-macro2 v1.0.86
-        │   └── unicode-ident v1.0.12
-        ├── quote v1.0.36
-        │   └── proc-macro2 v1.0.86 (*)
-        └── syn v2.0.72
-            ├── proc-macro2 v1.0.86 (*)
-            ├── quote v1.0.36 (*)
-            └── unicode-ident v1.0.12

According to cargo build --timings the eliminated dependencies account for 3.95s of the build time, which compares unfavourably with the entire aws-lc-sys build time (5.75s).

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.83%. Comparing base (c358484) to head (fbd5a18). Report is 41 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #467 +/- ## ========================================== - Coverage 95.80% 92.83% -2.97% ========================================== Files 61 62 +1 Lines 8143 8626 +483 Branches 0 8626 +8626 ========================================== + Hits 7801 8008 +207 - Misses 342 362 +20 - Partials 0 256 +256 ```

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