scm: Remove unused GitMergeError.

Not used after https://github.com/iterative/dvc/pull/9096

dvc/scm.py

@@ -20,7 +20,6 @@ from scmrepo.noscm import NoSCM
 
 from dvc.exceptions import DvcException
 from dvc.progress import Tqdm
-from dvc.utils import format_link
 
 if TYPE_CHECKING:
     from scmrepo.progress import GitProgressEvent
@@ -58,25 +57,6 @@ class GitAuthError(SCMError):
         super().__init__(f"{reason}\n{doc}")
 
 
-class GitMergeError(SCMError):
-    def __init__(self, msg: str, scm: Optional["Git"] = None) -> None:
-        if scm and self._is_shallow(scm):
-            url = format_link(
-                "https://dvc.org/doc/user-guide/troubleshooting#git-shallow"
-            )
-            msg = (
-                f"{msg}: `dvc exp` does not work in shallow Git repos. "
-                f"See {url} for more information."
-            )
-        super().__init__(msg)
-
-    @staticmethod
-    def _is_shallow(scm: "Git") -> bool:
-        if os.path.exists(os.path.join(scm.root_dir, Git.GIT_DIR, "shallow")):
-            return True
-        return False
-
-
 @contextmanager
 def map_scm_exception(with_cause: bool = False) -> Iterator[None]:
     from scmrepo.exceptions import SCMError as InternalSCMError

tests/unit/scm/test_scm.py

@@ -3,7 +3,7 @@ from datetime import datetime
 from scmrepo.exceptions import SCMError
 
 from dvc.repo.experiments import ExpRefInfo
-from dvc.scm import GitMergeError, iter_revs
+from dvc.scm import iter_revs
 
 
 def test_iter_revs(
@@ -99,11 +99,3 @@ def test_iter_revs(
         rev_old: [rev_old],
         rev_other: [rev_other],
     }
-
-
-def test_merge_error(tmp_dir, scm):
-    exc = GitMergeError("Merge failed")
-    assert "shallow" not in str(exc)
-    tmp_dir.gen({".git": {"shallow": ""}})
-    exc = GitMergeError("Merge failed", scm=scm)
-    assert "shallow" in str(exc)