core/rawdb: convert some comments to godoc convention (#21384)

core/rawdb/freezer.go

@@ -221,7 +221,7 @@ func (f *freezer) AppendAncient(number uint64, hash, header, body, receipts, td
 	return nil
 }
 
-// Truncate discards any recent data above the provided threshold number.
+// TruncateAncients discards any recent data above the provided threshold number.
 func (f *freezer) TruncateAncients(items uint64) error {
 	if atomic.LoadUint64(&f.frozen) <= items {
 		return nil
@@ -235,7 +235,7 @@ func (f *freezer) TruncateAncients(items uint64) error {
 	return nil
 }
 
-// sync flushes all data tables to disk.
+// Sync flushes all data tables to disk.
 func (f *freezer) Sync() error {
 	var errs []error
 	for _, table := range f.tables {