Revert "allow sha3 and keccak" and "fork 2: disable md5".

This reverts commit dd96449.
This reverts commit c26b38c.

multi-pow/src/lib.rs

@@ -331,25 +331,15 @@ impl FromStr for MaxiPosition {
     }
 }
 
-fn manual_fork_validation(parent_number: u32, algo: SupportedHashes) -> bool {
+fn manual_fork_validation(_parent_number: u32, algo: SupportedHashes) -> bool {
     use SupportedHashes::*;
 
-    // In the beginning there was md5 and it was good.
-    // On the second day we enabled sha3 and keccak and it was good.
-    if parent_number < 2300 {
-        match algo {
-            Md5 => true,
-            Sha3 => true,
-            Keccak => true,
-        }
-    } 
-    // On the third day we disable md5 and it was good
-    else {
-        match algo {
-            Md5 => false,
-            Sha3 => true,
-            Keccak => true,
-        }
+    // To begin with we only allow md5 hashes for our pow.
+    // After the fork height this check is skipped so all the hashes become valid.
+    match algo {
+        Md5 => true,
+        Sha3 => false,
+        Keccak => false,
     }
 }