Using Pluggable Transports on tor master is broken

While testing a patch for legacy/trac#21753 (moved) I realized that PTs in general are currently broken with tor master resulting into output like

CMETHOD obfs2 socks5 127.0.0.1:41925
CMETHOD obfs3 socks5 127.0.0.1:41299
CMETHOD obfs4 socks5 127.0.0.1:34025
CMETHOD scramblesuit socks5 127.0.0.1:35225
CMETHODS DONE'. We only support version '1'
Mar 16 13:03:05.000 [warn] Managed proxy at './TorBrowser/Tor/PluggableTransports/obfs4proxy' failed the configuration protocol and will be destroyed.

if started from Tor Browser.

Bisecting reveals that this got introduced with 6e78ede7 which fixed legacy/trac#21654 (moved).

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