[v10] Remove Drone Windows concurrency limit

[tcsc]

Windows builds are currently limited to 1 concurrent build for all stages
with the same name. This is causing unnecessary delay on the push build
queue, given that the Windows native builds are all set up to be independent
of one another.

Also updates the dronegen process to use a stock drone cli instance
proxied via tsh, to better match modern usage.

[codingllama]

Is this a problem for other versions and/or master? I see similar lines here, for example:

teleport/.drone.yml

Lines 914 to 939 in 7d40f37

	kind: pipeline
	type: exec
	name: build-native-windows-amd64
	trigger:
	event:
	include:
	- tag
	ref:
	include:
	- refs/tags/v*
	repo:
	include:
	- gravitational/*
	workspace:
	path: C:/Drone/Workspace/build-native-windows-amd64
	platform:
	os: windows
	arch: amd64
	node:
	buildbox_version: teleport13
	clone:
	disable: true
	depends_on:
	- clean-up-previous-build
	concurrency:
	limit: 1

I did find #21201 for v11, but no similar PRs for v12 or master.