doc: remove mention of `-rpctimeout` from man page
doc: remove mention of `-rpctimeout` from man page

That option hasn't existed for a long time.

Rebased-By: Wladimir J. van der Laan <bbc07dc96bb50bf6868a2ddfc4dae14fbed703d9@gmail.com>
Rebased-From: 381b25d

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