removes Default implementaion of ErasureConfig

The Default implementation of ErasureConfig is off and never useful:
https://github.com/solana-labs/solana/blob/150951333/ledger/src/erasure.rs#L49-L68

ledger/src/blockstore_meta.rs

@@ -46,7 +46,7 @@ pub struct ShredIndex {
     index: BTreeSet<u64>,
 }
 
-#[derive(Clone, Copy, Debug, Default, Deserialize, Serialize, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Deserialize, Serialize, Eq, PartialEq)]
 /// Erasure coding information
 pub struct ErasureMeta {
     /// Which erasure set in the slot this is
@@ -217,7 +217,8 @@ impl ErasureMeta {
         ErasureMeta {
             set_index,
             config,
-            ..Self::default()
+            __unused_first_coding_index: 0,
+            __unused_size: 0,
         }
     }
 
@@ -285,7 +286,7 @@ mod test {
         use ErasureMetaStatus::*;
 
         let set_index = 0;
-        let erasure_config = ErasureConfig::default();
+        let erasure_config = ErasureConfig::new(8, 16);
 
         let e_meta = ErasureMeta::new(set_index, erasure_config);
         let mut rng = thread_rng();

ledger/src/erasure.rs

@@ -46,27 +46,12 @@ use {
     serde::{Deserialize, Serialize},
 };
 
-//TODO(sakridge) pick these values
-/// Number of data shreds
-pub const NUM_DATA: usize = 8;
-/// Number of coding shreds; also the maximum number that can go missing.
-pub const NUM_CODING: usize = 8;
-
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
 pub struct ErasureConfig {
     num_data: usize,
     num_coding: usize,
 }
 
-impl Default for ErasureConfig {
-    fn default() -> ErasureConfig {
-        ErasureConfig {
-            num_data: NUM_DATA,
-            num_coding: NUM_CODING,
-        }
-    }
-}
-
 impl ErasureConfig {
     pub fn new(num_data: usize, num_coding: usize) -> ErasureConfig {
         ErasureConfig {
@@ -122,12 +107,6 @@ impl Session {
     }
 }
 
-impl Default for Session {
-    fn default() -> Session {
-        Session::new(NUM_DATA, NUM_CODING).unwrap()
-    }
-}
-
 #[cfg(test)]
 pub mod test {
     use super::*;