Drop CI for OpenSSL 1.0.2 (#953)

* Drop CI for OpenSSL 1.0.2

* Delete code for coverage reasons

* Bump minimum cryptography version
diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index 11be813..84f92b1 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -1603,16 +1603,8 @@
         if not isinstance(cert, X509):
             raise TypeError()
 
-        # As of OpenSSL 1.1.0i adding the same cert to the store more than
-        # once doesn't cause an error. Accordingly, this code now silences
-        # the error for OpenSSL < 1.1.0i as well.
-        if _lib.X509_STORE_add_cert(self._store, cert._x509) == 0:
-            code = _lib.ERR_peek_error()
-            err_reason = _lib.ERR_GET_REASON(code)
-            _openssl_assert(
-                err_reason == _lib.X509_R_CERT_ALREADY_IN_HASH_TABLE
-            )
-            _lib.ERR_clear_error()
+        res = _lib.X509_STORE_add_cert(self._store, cert._x509)
+        _openssl_assert(res == 1)
 
     def add_crl(self, crl):
         """