Remove manual of unsupported option (#2757)

contrib/windows/install-as-service.bat

@@ -1,25 +0,0 @@
-@ECHO off
-
-:: This script relies on nssm.exe to work.
-:: Please, download it and make it available on the system path,
-:: or copy it to the gogs path.
-:: https://nssm.cc/download
-:: This script itself should run in the gogs path, too.
-:: In case of startup failure, please read carefully the log file.
-:: Make sure Gitea work running manually with "gitea web" before running
-:: this script.
-:: And, please, read carefully the installation docs first:
-:: https://gogs.io/docs/installation
-:: To unistall the service, run "nssm remove gogs" and restart Windows.
-
-:: Set the folder where you extracted Gitea. Omit the last slash.
-SET gogspath=C:\gogs
-
-nssm install gogs "%gogspath%\gogs.exe"
-nssm set gogs AppParameters "web"
-nssm set gogs Description "A painless self-hosted Git service."
-nssm set gogs DisplayName "Gitea - Git with a cup of tea"
-nssm set gogs Start SERVICE_DELAYED_AUTO_START
-nssm set gogs AppStdout "%gogspath%\gogs.log"
-nssm start gogs
-pause