Drop unnecessary and broken handling of dotted FITS keys in WCS reads.

Writing keys with '.' in them isn't advisable, but HEIRARCH permits it
and we definitely don't want it to cause reading everything else to
fail.

src/geom/detail/frameSetUtils.cc

@@ -375,10 +375,8 @@ ast::FitsChan getFitsChanFromPropertyList(daf::base::PropertySet& metadata,
     }
 
     // Loop over the names and add them to the FitsChan if not excluded
-    for (auto const &fullName : allParamNames) {
-        if (excludeNames.count(fullName) == 0) {
-            std::size_t lastPeriod = fullName.rfind(char('.'));
-            auto name = (lastPeriod == std::string::npos) ? fullName : fullName.substr(lastPeriod + 1);
+    for (auto const &name : allParamNames) {
+        if (excludeNames.count(name) == 0) {
             std::type_info const &type = metadata.typeOf(name);
 
             if (name.size() > 8) {

tests/test_exposure.py

@@ -1150,6 +1150,15 @@ def testReadVersion2(self):
         self.assertEqual(reader.readExposureInfo().getPhotoCalib(), self.v1PhotoCalib)
         self.assertEqual(reader.readPhotoCalib(), self.v1PhotoCalib)
 
+    def testReadDottedHeaderKey(self):
+        """Test that we can read a file with a dot-delimited header key."""
+        original = afwImage.ExposureF.readFits(os.path.join(self.dataDir, "exposure-version-2.fits"))
+        original.metadata["x.y.z"] = "three"
+        with lsst.utils.tests.getTempFilePath(".fits") as tmpFile:
+            original.writeFits(tmpFile)
+            roundtripped = afwImage.ExposureF(tmpFile)
+        self.assertMaskedImagesEqual(original.maskedImage, roundtripped.maskedImage)
+
     def testExposureSummaryExtraComponents(self):
         """Test that we can read an exposure summary with extra components.
         """