Errata: remove numbers from headings

chapters/errata.adoc

@@ -81,7 +81,7 @@ are not cooperating to attack the network" it is perhaps more correct
 to say "as long as nodes cooperating to attack the network control less
 than about 30% of the network".
 
-=== 2. Transactions
+=== Transactions
 
 ____
 We define an electronic coin as a chain of digital signatures. Each
@@ -104,7 +104,7 @@ than one input and more than one output, the structure is not very
 chain-like; it’s more accurately described as a directed acyclic graph
 (DAG).
 
-=== 4. Proof-of-Work
+=== Proof-of-Work
 
 ____
 we implement the proof-of-work by incrementing a nonce in the block
@@ -150,7 +150,7 @@ Other implemented rules may further slow adjustments, such as a rule
 that the adjustment can not increase block production speed by more than
 300% per period, nor slow it by more than 75%.
 
-=== 7. Reclaiming Disk Space
+=== Reclaiming Disk Space
 
 ____
 Once the latest transaction in a coin is buried under enough blocks, the
@@ -165,7 +165,7 @@ data in the blockchain. This means the method described here cannot be
 universally used for reclaiming disk space among all nodes, as all new
 nodes will need to process all transactions.
 
-=== 8. Simplified Payment Verification
+=== Simplified Payment Verification
 
 ____
 One strategy to protect against this would be to accept alerts from
@@ -181,7 +181,7 @@ network nodes (full validation nodes) when invalid blocks have been
 detected. This has placed bitcoins in so-called SPV wallets at risk in
 the past.
 
-=== 10. Privacy
+=== Privacy
 
 ____
 Some linking is still unavoidable with multi-input transactions, which
@@ -200,7 +200,7 @@ This technique is known today as
 https://en.bitcoin.it/wiki/CoinJoin[CoinJoin] and software implementing
 it has been in use since 2015.
 
-=== 11. Calculations
+=== Calculations
 
 ____
 The receiver generates a new key pair and gives the public key to the