rugnux: no .ccp4 map files - the maps are given as coefficients in _maps.mtz only

A model validation no longer writes <prefix>_2fofc.ccp4, _fofc.ccp4 and _anom.ccp4 (nor their _mr
twins); <prefix>_maps.mtz, which Coot and PyMOL open as maps, is what is written. With the files
goes everything that only existed for them: ModelMaps keeps the coefficients alone, the
keep_map_grids switch is gone from the validation schedule and the rugnux config, and the
mFo-DFc map is no longer transformed to real space at all (nothing read it). The 2mFo-DFc and
anomalous maps are still made, for the mean atom density and the anomalous-site read-out.

The anomalous difference map is now in no output file: _maps.mtz carries no anomalous columns.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PXc1zD1yxHqaR1DGdCTHL4

tests/ModelValidationTest.cpp

@@ -574,10 +574,9 @@ TEST_CASE("ModelValidation_FindsTheDatasDescriptionOfTheLattice", "[ModelValidat
     const auto moved = ValidateAgainstModel(obs, data_cell, ReadModel(other_setting), logger, data_sg,
                                             /*probe_indexing_ambiguity=*/false, 1, 1.0);
     REQUIRE(moved.ok);
-    // The maps come back in memory: their coefficients always, the maps themselves only when asked for.
+    // The map coefficients come back in memory.
     REQUIRE(moved.maps);
     CHECK(moved.maps->coefficients.columns.size() == 12);
-    CHECK_FALSE(moved.maps->map_2fofc);
     logger.Info("Change of basis test: took {} out of {}, R-work {:.4f}",
                 moved.change_of_basis_op.triplet(), moved.setting_as_read, moved.r_work);
     CHECK_FALSE(moved.change_of_basis_op == gemmi::Op::identity());