tests(test_builder) Remove tmux 2.9 skip markers and cleanup imports

- Remove skip markers from test_layout_main_horizontal and
  test_issue_800_default_size_many_windows
- Remove unused has_lt_version import

These features are always available since tmux 3.2+ is now the
minimum version.

Author: tony

tests/workspace/test_builder.py

@@ -12,7 +12,6 @@
 import libtmux
 import pytest
 from libtmux._internal.query_list import ObjectDoesNotExist
-from libtmux.common import has_lt_version
 from libtmux.exc import LibTmuxException
 from libtmux.pane import Pane
 from libtmux.session import Session
@@ -1380,10 +1379,6 @@ def f(path: str, p: Pane) -> bool:
         assert retry_until(f_)
 
 
-@pytest.mark.skipif(
-    has_lt_version("2.9"),
-    reason="needs option introduced in tmux >= 2.9",
-)
 def test_layout_main_horizontal(session: Session) -> None:
     """Test that tmux's main-horizontal layout is used when specified."""
     yaml_workspace = test_utils.get_workspace_file("workspace/builder/three_pane.yaml")
@@ -1461,7 +1456,6 @@ class DefaultSizeNamespaceFixture(t.NamedTuple):
     DEFAULT_SIZE_FIXTURES,
     ids=[f.test_id for f in DEFAULT_SIZE_FIXTURES],
 )
-@pytest.mark.skipif(has_lt_version("2.9"), reason="default-size only applies there")
 def test_issue_800_default_size_many_windows(
     server: Server,
     monkeypatch: pytest.MonkeyPatch,