lib + cmds.projects: Use lib.Uri

Remove the feeble attempts at unifying URI handling, and use class Uri from lib.Uri instead.
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/ExecContext.py

@@ -243,14 +243,6 @@ class ExecContext(Base):
     def __init__(self, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
 
-    @abc.abstractmethod
-    def _username(self) -> str:
-        pass
-
-    @property
-    def username(self) -> str:
-        return self._username()
-
     async def run(
         self,
         cmd: list[str],