Avoid adding a redundant newline when printing weblistPageClosing (#665)

* Replace fmt.Println with fmt.Printf for newline-ending string.

This would otherwise be caught with the improved vet printf
checker (golang/go#30436).

* Replace fmt.Println with fmt.Printf for newline-ending string.

This would otherwise be caught with the improved vet printf
checker (golang/go#30436).

* Avoid adding a redundant newline when printing weblistPageClosing.

Author: zpavlinovic

internal/driver/testdata/pprof.cpu.flat.addresses.weblist

@@ -99,4 +99,3 @@ Duration: 10s, Total samples = 1.12s (11.20%)<br>Total: 1.12s</div><h2>line1000<
 
 </body>
 </html>
-

internal/report/source_html.go

@@ -72,5 +72,4 @@ function pprof_toggle_asm(e) {
 
 const weblistPageClosing = `
 </body>
-</html>
-`
+</html>`