refactor: remove unused OnDontHaveTimeout from cfg

After closer inspection it is not used for anything.  The one passed to
`newDontHaveTimeoutMgr` as a separate argument is used instead.

CHANGELOG.md

@@ -17,15 +17,18 @@ The following emojis are used to highlight certain changes:
 ### Added
 
 - `bitswap/client`: Improved timeout configuration for block requests
-  - Exposed `DontHaveTimeoutConfig` to hold configuration values for `dontHaveTimeoutMgr` which controls how long to wait for requested block, and if timeout should emit a synthetic DontHave response
+  - Exposed `DontHaveTimeoutConfig` to hold configuration values for `dontHaveTimeoutMgr` which controls how long to wait for requested block before emitting a synthetic DontHave response
   - Added `DefaultDontHaveTimeoutConfig()` to return a `DontHaveTimeoutConfig` populated with default values
   - Added optional `WithDontHaveTimeoutConfig` to allow passing a custom `DontHaveTimeoutConfig`
-  - If `DontHaveTimeoutConfig.onDontHaveTimeout` is `nil`, then `dontaHaveTimeoutMgr` is disabled and synthetic DontHave won't be emitted on timeout
+  - Setting `SetSendDontHaves(false)` works the same as before. Behind the scenes, it will disable `dontHaveTimeoutMgr` by passing a `nil` `onDontHaveTimeout` to `newDontHaveTimeoutMgr`.
+
 
 ### Changed
 
 ### Removed
 
+
+
 ### Fixed
 
 ### Security

bitswap/client/internal/messagequeue/donthavetimeoutmgr.go

@@ -12,9 +12,6 @@ import (
 )
 
 type DontHaveTimeoutConfig struct {
-	// OnDontHaveTimeout is the function called when DontHaveTimeout hits.
-	OnDontHaveTimeout func([]cid.Cid)
-
 	// DontHaveTimeout is used to simulate a DONT_HAVE when communicating with
 	// a peer whose Bitswap client doesn't support the DONT_HAVE response,
 	// or when the peer takes too long to respond.
@@ -49,10 +46,6 @@ type DontHaveTimeoutConfig struct {
 	clock clock.Clock
 }
 
-func (c *DontHaveTimeoutConfig) Enabled() bool {
-	return c.OnDontHaveTimeout != nil
-}
-
 func DefaultDontHaveTimeoutConfig() *DontHaveTimeoutConfig {
 	cfg := DontHaveTimeoutConfig{
 		DontHaveTimeout:            5 * time.Second,