Remove all the GParamSpec docs, since everything now uses the gtk-doc
docs instead, so there's no point in having two copies of each (which
are often out of sync anyway).

Since we're touching so many lines anyway, also fix up the indentation
of the remaining property-installing lines, and add
G_PARAM_STATIC_STRINGS to each paramspec (so the nick strings don't
get strduped). Also, be consistent about starting a new line between
"g_object_class_install_property" and its opening parenthesis.