Remove incorrect "default if no value provided" from timestamp docs

"us" is what "1" means, not what you get when no value is provided.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gpshead

Doc/using/cmdline.rst

@@ -712,7 +712,7 @@ Miscellaneous options
    * :samp:`-X traceback_timestamps=[us|ns|iso|0|1]` enables or configures timestamp
      display in exception tracebacks. When enabled, each exception's traceback
      will include a timestamp showing when the exception occurred. The format
-     options are: ``us`` (microseconds, default if no value provided), ``ns``
+     options are: ``us`` (microseconds), ``ns``
      (nanoseconds), ``iso`` (ISO-8601 formatted time), ``0`` (disable timestamps),
      and ``1`` (equivalent to ``us``). See also :envvar:`PYTHON_TRACEBACK_TIMESTAMPS`.
 

Python/initconfig.c

@@ -320,7 +320,7 @@ The following implementation-specific options are available:\n\
          for installed Python and \"off\" for a local build;\n\
          also PYTHON_FROZEN_MODULES\n\
 -X traceback_timestamps=[us|ns|iso|0|1]: display timestamp in tracebacks when\n\
-         exception occurs; \"us\" (default if no value provided) shows microseconds;\n\
+         exception occurs; \"us\" shows microseconds;\n\
          \"ns\" shows raw nanoseconds; \"iso\" shows ISO-8601 format; \"0\" disables timestamps;\n\
          \"1\" is equivalent to \"us\"; also PYTHON_TRACEBACK_TIMESTAMPS\n\
 "