Fix build on Windows (#2972)

plugins/inputs/system/processes.go

@@ -20,7 +20,6 @@ import (
 
 type Processes struct {
 	execPS       func() ([]byte, error)
-	getHostProc  func() string
 	readProcFile func(filename string) ([]byte, error)
 
 	forcePS   bool
@@ -63,14 +62,6 @@ func (p *Processes) Gather(acc telegraf.Accumulator) error {
 	return nil
 }
 
-func GetHostProc() string {
-	procPath := "/proc"
-	if os.Getenv("HOST_PROC") != "" {
-		procPath = os.Getenv("HOST_PROC")
-	}
-	return procPath
-}
-
 // Gets empty fields of metrics based on the OS
 func getEmptyFields() map[string]interface{} {
 	fields := map[string]interface{}{