logtail/filch: use bufio.ScanLines

splitLines here is identical to bufio.ScanLines,
except that bufio.ScanLines removes \r in addition to \n.
Trailing carriage returns shouldn't matter for our uses.
Since bufio.ScanLines is the default for a new bufio.Scanner,
we can delete the calls to Split too.

logtail/filch/filch.go

@@ -8,7 +8,6 @@ package filch
 
 import (
 	"bufio"
-	"bytes"
 	"fmt"
 	"io"
 	"os"
@@ -53,7 +52,6 @@ func (f *Filch) TryReadLine() ([]byte, error) {
 		return nil, err
 	}
 	f.altscan = bufio.NewScanner(f.alt)
-	f.altscan.Split(splitLines)
 	return f.scan()
 }
 
@@ -188,7 +186,6 @@ func New(filePrefix string, opts Options) (f *Filch, err error) {
 	}
 	if f.recovered > 0 {
 		f.altscan = bufio.NewScanner(f.alt)
-		f.altscan.Split(splitLines)
 	}
 
 	f.OrigStderr = nil
@@ -228,16 +225,3 @@ func moveContents(dst, src *os.File) (err error) {
 	}
 	return nil
 }
-
-func splitLines(data []byte, atEOF bool) (advance int, token []byte, err error) {
-	if atEOF && len(data) == 0 {
-		return 0, nil, nil
-	}
-	if i := bytes.IndexByte(data, '\n'); i >= 0 {
-		return i + 1, data[0 : i+1], nil
-	}
-	if atEOF {
-		return len(data), data, nil
-	}
-	return 0, nil, nil
-}