SCUBA2: ensure correct config parameters for OMC1

OMC1 is sometimes used as a pointing source, but due to it being
extended, it is not appropriate to use the standard pointing config
file. The previousy pointing_extended config file has now been
deleted, so its parameters must be provided by the pipeline. However,
there is an additional wrinkle in that the CADC processing of OMC1
poitings must use bright_extended.

_SCUBA2_HELLO_ now does not set the makemap config type to
pointing_extended.

_GET_MAKEMAP_CONFIG_ now appends the relevant parameters to the
default config returned for makemap.

_REDUCE_SCAN_STEER_ now sets the config type to bright_extended for
OMC1 pointings, unless the user has provided a config file.

These three updates should enable the pipeline to always do the right
thing for OMC1 pointing data.