Do not free SSL_COMP_get_compression_methods() directly

A regression caused by bug 1341067 fix:

"Arkadiusz Miśkiewicz (arekm) wrote 11 hours ago: #1
This causes collision when using php which loads mysql module (linked with percona libs) and curl module (that uses libcurl). Both, percona and curl are trying to free the same global data.

https://github.com/curl/curl/issues/905

Why percona doesn't use proper API - SSL_COMP_free_compression_methods() ?

SSL_COMP_free_compression_methods() uses sk_pop_free() which is protected from double free.

--- percona-server-5.6.28-76.1/vio/vio.c~ 2016-01-08 23:12:24.000000000 +0100
+++ percona-server-5.6.28-76.1/vio/vio.c 2016-07-19 18:54:23.648042457 +0200
@@ -399,6 +399,6 @@ void vio_end(void)
   ERR_free_strings();
   EVP_cleanup();
   CRYPTO_cleanup_all_ex_data();
- sk_SSL_COMP_free(SSL_COMP_get_compression_methods());
+ SSL_COMP_free_compression_methods();
 #endif
 }"