Remove redundant code for Python <= 3.6

Author: hugovk

src/prompt_toolkit/application/application.py

@@ -999,7 +999,7 @@ def _enable_breakpointhook(self) -> Generator[None, None, None]:
         manager. (We will only install the hook if no other custom hook was
         set.)
         """
-        if sys.version_info >= (3, 7) and sys.breakpointhook == sys.__breakpointhook__:
+        if sys.breakpointhook == sys.__breakpointhook__:
             sys.breakpointhook = self._breakpointhook
 
             try:

src/prompt_toolkit/application/current.py

@@ -145,12 +145,8 @@ def create_app_session(
     Create a separate AppSession.
 
     This is useful if there can be multiple individual `AppSession`s going on.
-    Like in the case of an Telnet/SSH server. This functionality uses
-    contextvars and requires at least Python 3.7.
+    Like in the case of an Telnet/SSH server.
     """
-    if sys.version_info <= (3, 6):
-        raise RuntimeError("Application sessions require Python 3.7.")
-
     # If no input/output is specified, fall back to the current input/output,
     # whatever that is.
     if input is None: