Drop some explicit SSLKeyShare destructors.

We zero out memory in |OPENSSL_free| already.

Change-Id: I84a0f3cdfadd4544c0fade1d3d727baa6496ffe5
Reviewed-on: https://boringssl-review.googlesource.com/c/33446
Commit-Queue: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

ssl/ssl_key_share.cc

diff --git a/ssl/ssl_key_share.cc b/ssl/ssl_key_share.cc
index 80b7d0a..55c7463 100644
--- a/ssl/ssl_key_share.cc
+++ b/ssl/ssl_key_share.cc
@@ -38,7 +38,6 @@
 class ECKeyShare : public SSLKeyShare {
  public:
   ECKeyShare(int nid, uint16_t group_id) : nid_(nid), group_id_(group_id) {}
-  ~ECKeyShare() override {}
 
   uint16_t GroupID() const override { return group_id_; }
 
@@ -159,9 +158,6 @@
 class X25519KeyShare : public SSLKeyShare {
  public:
   X25519KeyShare() {}
-  ~X25519KeyShare() override {
-    OPENSSL_cleanse(private_key_, sizeof(private_key_));
-  }
 
   uint16_t GroupID() const override { return SSL_CURVE_X25519; }