Remove IOError

Since Python 3.3 IOError is an alias of OSError and is kept for
compatibility. No longer needed since the project supports
only bigger Python versions.

Signed-off-by: Teodora Sechkova <tsechkova@vmware.com>

securesystemslib/storage.py

@@ -200,7 +200,7 @@ def get(self, filepath:str) -> Generator[BinaryIO, None, None]:
     try:
       file_object = open(filepath, 'rb')
       yield file_object
-    except (FileNotFoundError, IOError):
+    except OSError:
       raise exceptions.StorageError(
           "Can't open %s" % filepath)
     finally:
@@ -221,7 +221,7 @@ def put(self, fileobj: IO, filepath: str) -> None:
         # and the operating system's buffers.  os.fsync() should follow flush().
         destination_file.flush()
         os.fsync(destination_file.fileno())
-    except (OSError, IOError):
+    except OSError:
       raise exceptions.StorageError(
           "Can't write file %s" % filepath)