Drop redundant coverage exclusion markers in the excluded tail region

`getNodeSize`'s unreachable `default:` sits inside ConflictSet.cpp's
`GCOVR_EXCL_START`/`GCOVR_EXCL_STOP` block, so the `GCOVR_EXCL_LINE` markers on
those two lines are redundant: they cannot change the report, but they make
gcovr print

    (WARNING) GCOVR_EXCL_LINE found on line 6002 in excluded region started on
    line 5535

once per line for each of the four reports the coverage job writes. Drop them,
matching the rest of the excluded tail, which carries no exclusion markers.

Context: the previous coverage job for this branch did not fail in any of its
steps. Build, Test (5754/5754 passed), Coverage report (`gcovr
--fail-under-line 100` reported 100% for ConflictSet.cpp, LongestCommonPrefix.h
and Metrics.h), the upload and the test summary all reported success; the job
was marked failed while tearing the job container down. The post-actions
(actions/cache, actions/checkout) could no longer `docker exec` into the
container and the runner's rootless podman socket was gone ("Cannot connect to
the Docker daemon at unix:///run/user/992/podman/podman.sock", "Error while stop
job container"); the actions/cache service on 192.168.0.110:41379 had been
refusing connections for the whole run.

Verified locally on this commit: Debug, gcc and `--coverage` builds of the
coverage job's configuration; 5754/5754 tests pass; merged line coverage (union
over the library, SHOW_MEMORY and fuzz-driver objects, honouring the
GCOVR_EXCL_START/STOP regions) is 100% for all three measured files, and no
GCOVR_EXCL_LINE markers remain inside an excluded region.

ConflictSet.cpp

@@ -5999,8 +5999,8 @@ int64_t getNodeSize(struct Node *n) {
     return sizeof(Node48);
   case Type_Node256:
     return sizeof(Node256);
-  default:   // GCOVR_EXCL_LINE
-    abort(); // GCOVR_EXCL_LINE
+  default:
+    abort();
   }
 }