refactor!: keep one name for pending updates, drop the alias

This driver implemented get_pending_updates and then carried
get_available_updates as a one-line alias, because netOrk's API only ever called
the latter. Two names for one thing, with the driver bridging the gap.

napalm-device-types v1.0 collapses them onto get_available_updates — the name
four drivers and every netOrk call site already used — so the alias has nothing
left to bridge.

BREAKING CHANGE: get_pending_updates is gone; call get_available_updates.

The seven pre-existing test failures in this repo are untouched and unrelated;
see netork#110.

tests/test_linux.py

@@ -166,7 +166,7 @@ def test_get_packages_apt(driver):
 
 
 # ---------------------------------------------------------------------------
-# get_pending_updates (apt)
+# get_available_updates (apt)
 # ---------------------------------------------------------------------------
 
 
@@ -177,10 +177,10 @@ APT_UPGRADABLE = (
 )
 
 
-def test_get_pending_updates_apt(driver):
+def test_get_available_updates_apt(driver):
     driver._pkg_manager = "apt"
     with patch.object(driver, "_send", side_effect=["", APT_UPGRADABLE]):
-        updates = driver.get_pending_updates()
+        updates = driver.get_available_updates()
     assert len(updates) == 2
     assert updates[0]["name"] == "openssh-server"
     assert updates[0]["current_version"] == "1:9.2p1-2+deb12u1"