Remove unnecessary override of write_async_safe

pager_file overrides write_async_safe but does so in the same way as
its superclass.  So, remove the unnecessary override.

Approved-By: Andrew Burgess <aburgess@redhat.com>

gdb/pager.h

diff --git a/gdb/pager.h b/gdb/pager.h
index a23e1bc..5d64ffc 100644
--- a/gdb/pager.h
+++ b/gdb/pager.h
@@ -44,11 +44,6 @@ class pager_file : public wrapped_file
 
   void puts (const char *str) override;
 
-  void write_async_safe (const char *buf, long length_buf) override
-  {
-    m_stream->write_async_safe (buf, length_buf);
-  }
-
   void emit_style_escape (const ui_file_style &style) override;
 
   void flush () override;