refactor(ephemeris): Use ch_ephem

This re-imports stuff moved to `ch_ephem`.  It both
re-imports everything that was moved back into `ch_util.ephemeris` for
backwards compatibility, but also removes references to
`ch_util.epheremis` from the code, using the newly-exported versions
of things directly.

This PR requires both:

* radiocosmology/caput#271
* chime-experiment/ch_ephem#1

Catalogs:

All the catalogs have been moved to `ch_ephem`, which provides a
standard interface to them via `ch_ephem.catalogs.load`.  To make this
change, `fluxcat.FluxCatalog.load` has been broken into two pieces.  The
new `fluxcat.FluxCatalog.load_dict` imports a catalog from an
already-parsed JSON dict (which is what `ch_ephem` provides).  The
original `fluxcat.FluxCatalog.load` works as it used to, but tail-calls
`load_dict` to do most of the importing.

Position data:

Position data (lat, lon, alt) is now obtained by fetching the parameter
out of the `caput.time.Observer` objects provided by `ch_ephem`.  The
constants in `ch_util.ephemeris` are populated by doing this.

Instrument geormetry:

`ch_ephem` has also taken on the geometry data (rotation, roll, offset)
that was in `tools` (where it's been re-imported from `ch_ephem`).

Private objects deleted:

I've also deleted a number of private objects which are no longer
being used (i.e. objects whose names start with a leading underscore).

Notable among these are the geometry constants from `ch_util.tools`
and the unused`ch_util.tools._LAT_LON` which had position data for
various instruments which differed from the position data provided
by `ch_util.ephemeris`.

Also removed are the long-deprectated `ch_util.ephemeris._get_chime` and
`ch_util.ephemeris.transit_RA`.

ch_util/cal_utils.py

@@ -17,9 +17,14 @@
 from scipy.linalg import lstsq, inv
 
 from caput import memh5, time as ctime
+
 from chimedb import dataset as ds
 from chimedb.dataset.utils import state_id_of_type, unique_unmasked_entry
-from ch_util import ephemeris, tools
+
+from ch_ephem.observers import chime
+import ch_ephem.sources
+
+from ch_util import tools
 
 # Set up logging
 logger = logging.getLogger(__name__)
@@ -2474,13 +2479,13 @@ def thermal_amplitude(delta_T, freq):
 def _el_to_dec(el):
     """Convert from el = sin(zenith angle) to declination in degrees."""
 
-    return np.degrees(np.arcsin(el)) + ephemeris.CHIMELATITUDE
+    return np.degrees(np.arcsin(el)) + chime.latitude
 
 
 def _dec_to_el(dec):
     """Convert from declination in degrees to el = sin(zenith angle)."""
 
-    return np.sin(np.radians(dec - ephemeris.CHIMELATITUDE))
+    return np.sin(np.radians(dec - chime.latitude))
 
 
 def get_reference_times_file(
@@ -2691,10 +2696,10 @@ def get_reference_times_dataset_id(
 
     # The CHIME calibration sources
     _source_dict = {
-        "cyga": ephemeris.CygA,
-        "casa": ephemeris.CasA,
-        "taua": ephemeris.TauA,
-        "vira": ephemeris.VirA,
+        "cyga": ch_ephem.sources.CygA,
+        "casa": ch_ephem.sources.CasA,
+        "taua": ch_ephem.sources.TauA,
+        "vira": ch_ephem.sources.VirA,
     }
 
     # Get the set of gain IDs for each time stamp
@@ -2728,9 +2733,7 @@ def get_reference_times_dataset_id(
 
         # Calculate the source transit time, and sanity check it
         source = _source_dict[d["source_name"]]
-        d["source_transit"] = ephemeris.transit_times(
-            source, d["gen_time"] - 24 * 3600.0
-        )
+        d["source_transit"] = chime.transit_times(source, d["gen_time"] - 24 * 3600.0)
         cal_diff_hours = (d["gen_time"] - d["source_transit"]) / 3600
         if cal_diff_hours > 3:
             logger.warn(