build: update logging statements to make json log work - fixes #6038

This changes log statements from log to fs package, which is required for --use-json-log
to properly make log output in JSON format. The recently added custom linting rule,
handled by ruleguard via gocritic via golangci-lint, warns about these and suggests
the alternative. Fixing was therefore basically running "golangci-lint run --fix",
although some manual fixup of mainly imports are necessary following that.

cmd/rcat/rcat.go

@@ -3,11 +3,11 @@ package rcat
 
 import (
 	"context"
-	"log"
 	"os"
 	"time"
 
 	"github.com/rclone/rclone/cmd"
+	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config/flags"
 	"github.com/rclone/rclone/fs/operations"
 	"github.com/spf13/cobra"
@@ -64,7 +64,7 @@ destination which can use retries.`,
 
 		stat, _ := os.Stdin.Stat()
 		if (stat.Mode() & os.ModeCharDevice) != 0 {
-			log.Fatalf("nothing to read from standard input (stdin).")
+			fs.Fatalf(nil, "nothing to read from standard input (stdin).")
 		}
 
 		fdst, dstFileName := cmd.NewFsDstFile(args)