Let grpc do validation instead of typeguard

Typeguard does not seem to work on Optional[str]
as

```python

from typing import Optional
from typeguard import typechecked

@TypeChecked()
def foo(filename: Optional[str] = None) -> None:
   print(filename)

foo(42)
```
Raises no error

grpc4bmi/bmi_grpc_client.py

@@ -9,7 +9,6 @@
 from bmipy import Bmi
 import grpc
 import numpy
-from typeguard import typechecked
 
 from grpc_status import rpc_status
 from google.rpc import error_details_pb2
@@ -94,7 +93,6 @@ def get_unique_port(host=None):
             s.bind(("" if host is None else host, 0))
             return int(s.getsockname()[1])
 
-    @typechecked
     def initialize(self, filename: Optional[str]):
         fname = "" if filename is None else filename
         try:

test/test_client.py

@@ -9,7 +9,6 @@
 from google.rpc import error_details_pb2, status_pb2, code_pb2
 from grpc_status import rpc_status
 from heat import BmiHeat
-from typeguard import TypeCheckError
 
 from grpc4bmi.bmi_grpc_server import BmiServer
 from grpc4bmi.bmi_grpc_client import BmiClient, RemoteException, handle_error
@@ -109,7 +108,7 @@ def test_initialize():
 def test_initialize_with_nonstring():
     client, local = make_bmi_classes(False)
     assert client is not None
-    with pytest.raises(TypeCheckError, match='did not match any element in the union'):
+    with pytest.raises(TypeError, match='bad argument type for built-in operation'):
         client.initialize(42)
     client.finalize()
     del client