python: Remove unnecessary NonBinaryStr TypeVar.

This was a potentially useful value (later superceded by use of Text)
when first introduced, but now that we're on Python 3, it should just
be str.

zerver/lib/db.py

@@ -4,7 +4,6 @@ from psycopg2.extensions import cursor, connection
 
 from typing import Callable, Optional, Iterable, Any, Dict, List, Union, TypeVar, \
     Mapping
-from zerver.lib.str_utils import NonBinaryStr
 
 CursorObj = TypeVar('CursorObj', bound=cursor)
 ParamsT = Union[Iterable[Any], Mapping[str, Any]]
@@ -12,8 +11,8 @@ ParamsT = Union[Iterable[Any], Mapping[str, Any]]
 # Similar to the tracking done in Django's CursorDebugWrapper, but done at the
 # psycopg2 cursor level so it works with SQLAlchemy.
 def wrapper_execute(self: CursorObj,
-                    action: Callable[[NonBinaryStr, Optional[ParamsT]], CursorObj],
-                    sql: NonBinaryStr,
+                    action: Callable[[str, Optional[ParamsT]], CursorObj],
+                    sql: str,
                     params: Optional[ParamsT]=()) -> CursorObj:
     start = time.time()
     try:
@@ -28,11 +27,11 @@ def wrapper_execute(self: CursorObj,
 class TimeTrackingCursor(cursor):
     """A psycopg2 cursor class that tracks the time spent executing queries."""
 
-    def execute(self, query: NonBinaryStr,
+    def execute(self, query: str,
                 vars: Optional[ParamsT]=None) -> 'TimeTrackingCursor':
         return wrapper_execute(self, super().execute, query, vars)
 
-    def executemany(self, query: NonBinaryStr,
+    def executemany(self, query: str,
                     vars: Iterable[Any]) -> 'TimeTrackingCursor':
         return wrapper_execute(self, super().executemany, query, vars)