mail/imapfilter: Drop LibreSSL patch and unbreak build with OpenSSL 1.1.1

The patch added in ports r435498 broke OpenSSL 1.1.x compatibility.
A different fix for LibreSSL was committed upstream so the patch
is no longer needed since imapfilter 2.6.11 [1].

[1] c1865ba1ab

PR:		232132
Approved by:	bofh (maintainer timeout, 1 month)

mail/imapfilter/files/patch-src_auth.c

@@ -1,20 +0,0 @@
---- src/auth.c.orig	2017-11-19 09:38:24 UTC
-+++ src/auth.c
-@@ -20,7 +20,7 @@ auth_cram_md5(const char *user, const char *pass, unsi
- 	unsigned char *resp, *buf, *out;
- 	unsigned char md[EVP_MAX_MD_SIZE], mdhex[EVP_MAX_MD_SIZE * 2 + 1];
- 	unsigned int mdlen;
--#if OPENSSL_VERSION_NUMBER >= 0x1010000fL && !defined(LIBRESSL_VERSION_NUMBER)
-+#ifdef HAVE_OPAQUE_STRUCTS && !defined(LIBRESSL_VERSION_NUMBER)
- 	HMAC_CTX *ctx;
- #else
- 	HMAC_CTX ctx;
-@@ -32,7 +32,7 @@ auth_cram_md5(const char *user, const char *pass, unsi
- 
- 	EVP_DecodeBlock(resp, chal, strlen((char *)(chal)));
- 
--#if OPENSSL_VERSION_NUMBER >= 0x1010000fL && !defined(LIBRESSL_VERSION_NUMBER)
-+#ifdef HAVE_OPAQUE_STRUCTS && !defined(LIBRESSL_VERSION_NUMBER)
- 	ctx = HMAC_CTX_new();
- 	HMAC_Init_ex(ctx, (const unsigned char *)pass, strlen(pass),
- 	    EVP_md5(), NULL);