Adding no-op X509_TRUST_cleanup for select application compatibility (aws#2257)

### Description of changes:
- Re-implements X509_TRUST_cleanup() as a No-Op function after previous
removal
- Function was removed in commit #74c1f2a but is needed for select
consuming applications
- Added documentation explaining AWS-LC's different approach to trust
settings

### Testing:
- No regression testing needed (No-Op implementation)

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.

Author: kingstjo

crypto/x509/x509_trs.c

@@ -139,6 +139,16 @@ char *X509_TRUST_get0_name(const X509_TRUST *xp) { return xp->name; }
 
 int X509_TRUST_get_trust(const X509_TRUST *xp) { return xp->trust; }
 
+void X509_TRUST_cleanup(void) {
+      // This is an intentional No-Op (no operation) function.
+      //
+      // Historical Context:
+      // - This function existed in OpenSSL versions prior to 1.1.0
+      // - AWS-LC does not support static trust settings storage
+      //
+      // - Kept for API compatibility with older versions
+}
+
 static int trust_1oidany(const X509_TRUST *trust, X509 *x) {
   if (x->aux && (x->aux->trust || x->aux->reject)) {
     return obj_trust(trust->arg1, x);

include/openssl/x509.h

@@ -5090,6 +5090,11 @@ OPENSSL_EXPORT int X509_TRUST_get_by_id(int id);
 OPENSSL_EXPORT int X509_TRUST_get_flags(const X509_TRUST *xp);
 OPENSSL_EXPORT char *X509_TRUST_get0_name(const X509_TRUST *xp);
 OPENSSL_EXPORT int X509_TRUST_get_trust(const X509_TRUST *xp);
+// X509_TRUST_cleanup intentionally does nothing.
+// This function is maintained only for compatibility with applications
+// that consume OpenSSL APIs. AWS-LC does not support the related
+// static trust settings functions which were also deprecated in OpenSSL 1.1.0.
+OPENSSL_EXPORT OPENSSL_DEPRECATED void X509_TRUST_cleanup(void);
 
 #define X509_LU_NONE 0
 #define X509_LU_X509 1