Remove `USE_OPENSSL_BASE64` and the associated code.

The alternative has been available since 2007, there's no way to
actually enable the ifdef, and it breaks on well formed but not OpenSSL
style inputs.

changes/feature15652

+  o Removed code:
+    - Remove `USE_OPENSSL_BASE64` and the corresponding fallback code and
+      always use the internal Base64 decoder. The internal decoder has been
+      part of tor since tor-0.2.0.10-alpha, and no one should be using the
+      OpenSSL one. Part of ticket 15652.

src/common/crypto.c

@@ -2500,26 +2500,6 @@ static const uint8_t base64_decode_table[256] = {
 int
 base64_decode(char *dest, size_t destlen, const char *src, size_t srclen)
 {
-#ifdef USE_OPENSSL_BASE64
-  EVP_ENCODE_CTX ctx;
-  int len, ret;
-  /* 64 bytes of input -> *up to* 48 bytes of output.
-     Plus one more byte, in case I'm wrong.
-  */
-  if (destlen < ((srclen/64)+1)*49)
-    return -1;
-  if (destlen > SIZE_T_CEILING)
-    return -1;
-
-  memset(dest, 0, destlen);
-
-  EVP_DecodeInit(&ctx);
-  EVP_DecodeUpdate(&ctx, (unsigned char*)dest, &len,
-                   (unsigned char*)src, srclen);
-  EVP_DecodeFinal(&ctx, (unsigned char*)dest, &ret);
-  ret += len;
-  return ret;
-#else
   const char *eos = src+srclen;
   uint32_t n=0;
   int n_idx=0;
@@ -2590,7 +2570,6 @@ base64_decode(char *dest, size_t destlen, const char *src, size_t srclen)
   tor_assert((dest-dest_orig) <= INT_MAX);
 
   return (int)(dest-dest_orig);
-#endif
 }
 #undef X
 #undef SP
@@ -2615,23 +2594,10 @@ digest_to_base64(char *d64, const char *digest)
 int
 digest_from_base64(char *digest, const char *d64)
 {
-#ifdef USE_OPENSSL_BASE64
-  char buf_in[BASE64_DIGEST_LEN+3];
-  char buf[256];
-  if (strlen(d64) != BASE64_DIGEST_LEN)
-    return -1;
-  memcpy(buf_in, d64, BASE64_DIGEST_LEN);
-  memcpy(buf_in+BASE64_DIGEST_LEN, "=\n\0", 3);
-  if (base64_decode(buf, sizeof(buf), buf_in, strlen(buf_in)) != DIGEST_LEN)
-    return -1;
-  memcpy(digest, buf, DIGEST_LEN);
-  return 0;
-#else
   if (base64_decode(digest, DIGEST_LEN, d64, strlen(d64)) == DIGEST_LEN)
     return 0;
   else
     return -1;
-#endif
 }
 
 /** Base64 encode DIGEST256_LINE bytes from <b>digest</b>, remove the
@@ -2653,23 +2619,10 @@ digest256_to_base64(char *d64, const char *digest)
 int
 digest256_from_base64(char *digest, const char *d64)
 {
-#ifdef USE_OPENSSL_BASE64
-  char buf_in[BASE64_DIGEST256_LEN+3];
-  char buf[256];
-  if (strlen(d64) != BASE64_DIGEST256_LEN)
-    return -1;
-  memcpy(buf_in, d64, BASE64_DIGEST256_LEN);
-  memcpy(buf_in+BASE64_DIGEST256_LEN, "=\n\0", 3);
-  if (base64_decode(buf, sizeof(buf), buf_in, strlen(buf_in)) != DIGEST256_LEN)
-    return -1;
-  memcpy(digest, buf, DIGEST256_LEN);
-  return 0;
-#else
   if (base64_decode(digest, DIGEST256_LEN, d64, strlen(d64)) == DIGEST256_LEN)
     return 0;
   else
     return -1;
-#endif
 }
 
 /** Implements base32 encoding as in RFC 4648.  Limitation: Requires