Docs: Fix some broken links to deleted doc sections

Author: andypugh

docs/src/getting-started/updating-linuxcnc.adoc

@@ -275,7 +275,10 @@ ton
 
 A framework for controlling ModBus devices using the serial ports on
 many Mesa cards has been introduced.
+http://linuxcnc.org/docs/2.9/html/drivers/mesa_modbus.html
 
 A new GPIO driver for any GPIO which is supported by the gpiod library
 is now included:
+http://linuxcnc.org/docs/2.9/html/drivers/hal_gpio.html
+
 

docs/src/gui/qtvcp-widgets.adoc

@@ -1876,8 +1876,7 @@ Enter any of these _case sensitive_ commands to load the respective program or a
   link:../man/man1/linuxcnctop.1.html[`status`] utility.
 *`CALIBRATION`*::
   Starts LinuxCNC
-  link:../getting-started/updating-linuxcnc.html#_calibration_emccalib_tcl[calibration]
-  utility.
+  emccalib_tcl[calibration] utility.
 *`CLASSICLADDER`*::
   Starts the link:../ladder/classic-ladder.html[ClassicLadder GUI] if the _ClassicLadder realtime HAL component_ was loaded by the machine's config files.
 *`PREFERENCE`*::

docs/src/plasma/qtplasmac.adoc

@@ -1286,7 +1286,7 @@ Some standard LinuxCNC utilities are provided as an aid in the diagnosis of issu
 - link:../hal/halshow.html#cha:halshow[Halshow]
 - link:../hal/tutorial.html#sec:tutorial-halscope[Halscope]
 - link:../hal/tutorial.html#sec:tutorial-halmeter[Halmeter]
-- link:../getting-started/updating-linuxcnc.html#_calibration_emccalib_tcl[Calibration]
+- Calibration assistant (emccalib.tcl).
 - link:../man/man1/linuxcnctop.1.html[Status]
 
 In addition the following two QtPlasmaC specific utilities are provided: