Fix comment in sha2.h

An incorrect reference to SHA-1 was present.

Author: Daniel Gustafsson
Discussion: https://postgr.es/m/FE26C953-FA87-4BB9-9105-AA1F8705B0D0@yesql.se

Author: michaelpq

src/include/common/sha2.h

@@ -68,7 +68,7 @@
 #define PG_SHA512_DIGEST_LENGTH			64
 #define PG_SHA512_DIGEST_STRING_LENGTH	(PG_SHA512_DIGEST_LENGTH * 2 + 1)
 
-/* Context Structures for SHA-1/224/256/384/512 */
+/* Context Structures for SHA224/256/384/512 */
 #ifdef USE_OPENSSL
 typedef SHA256_CTX pg_sha256_ctx;
 typedef SHA512_CTX pg_sha512_ctx;