Merge branch 'js/misc-doc-fixes'

"make check-docs", "git help -a", etc. did not account for cases
where a particular build may deliberately omit some subcommands,
which has been corrected.

* js/misc-doc-fixes:
  Turn `git serve` into a test helper
  test-tool: handle the `-C <directory>` option just like `git`
  check-docs: do not bother checking for legacy scripts' documentation
  docs: exclude documentation for commands that have been excluded
  check-docs: allow command-list.txt to contain excluded commands
  help -a: do not list commands that are excluded from the build
  Makefile: drop the NO_INSTALL variable
  remote-testgit: move it into the support directory for t5801

git.c

@@ -570,7 +570,6 @@ static struct cmd_struct commands[] = {
 	{ "revert", cmd_revert, RUN_SETUP | NEED_WORK_TREE },
 	{ "rm", cmd_rm, RUN_SETUP },
 	{ "send-pack", cmd_send_pack, RUN_SETUP },
-	{ "serve", cmd_serve, RUN_SETUP },
 	{ "shortlog", cmd_shortlog, RUN_SETUP_GENTLY | USE_PAGER },
 	{ "show", cmd_show, RUN_SETUP },
 	{ "show-branch", cmd_show_branch, RUN_SETUP },