Remove gufe submodule and fix pydantic import

gufe v1.2.0 is available on conda-forge, no longer need the submodule
for testing.

pydantic imports now match the style used in gufe to address version issue.

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "lib/gufe"]
-	path = lib/gufe
-	url = [email protected]:OpenFreeEnergy/gufe

src/stratocaster/strategies/connectivity.py

@@ -1,10 +1,20 @@
 from gufe import AlchemicalNetwork, ProtocolResult
 from gufe.tokenization import GufeKey
-from pydantic import Field, root_validator, validator
 
 from stratocaster.base import Strategy, StrategyResult
 from stratocaster.base.models import StrategySettings
 
+try:
+    from pydantic.v1 import Field, root_validator, validator
+except ImportError:
+    from pydantic import (
+        Field,
+        root_validator,
+        validator,
+    )
+
+import pydantic
+
 
 # TODO: docstrings
 class ConnectivityStrategySettings(StrategySettings):