config: Increase mountain process efficiency from 75% to 100%

config: Increase mountain process efficiency from 75% to 100%

Each point of gold resource is worth 5d.  Except for mountains, where
it's just 3.75d.  This is because a mountain's process efficiency is
only 75%.  Has been that way since Empire 3 made mountains mine gold.

This is actually a needless complication: a sector with 75% process
efficiency produces just like one with 100% process efficiency and 75%
of the resource.

Increase mountain process efficiency to 100%.  Deities may want to
compensate by adjusting mountains' gold resources.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>