Remove TAP-Windows driver from installer, and update docs to reference Wintun's default inclusion
@dlenski, this re-applies your commit 8c1d2de0 from !178 (merged), later reverted by b5ff6f3f.
@dlenski, this re-applies your commit 8c1d2de0 from !178 (merged), later reverted by b5ff6f3f.