Remove docs for joystick slider as it now is in core (#80)

* Remove docs for joystick slider as it now is in core

* Remove reference to joystick slider

docs/web-configurator/menu-pages/02-pin-mapping.mdx

@@ -16,8 +16,8 @@ Here you can remap the GP2040-CE buttons to different GPIO pins on the RP2040 ch
 The following options are available for assignment to each GPIO Pin.
 
 - Standard Gamepad inputs found in [Buttons](../../usage.mdx#buttons)
+- D-Pad Mode: Digital, Left Stick, and Right Stick
 - [Dual Direction Input](../../add-ons/dual-direction-input.mdx) Up, Down, Left and Right
-- [D-Pad Mode](../../add-ons/joystick-selection-slider.mdx): Digital, Left Stick, and Right Stick
 - [Up Priority SOCD Cleaning](../../hotkeys.mdx#socd-up-priority)
 - [Neutral SOCD Cleaning](../../hotkeys.mdx#socd-neutral)
 - [Last Win SOCD Cleaning](../../hotkeys.mdx#socd-last-win)

docs/web-configurator/menu-pages/08-add-ons-configuration.mdx

@@ -27,7 +27,6 @@ Some of these add-ons are experimental and not all add-ons are interoperable wit
 - [I2C Analog ADS1219](../../add-ons/i2c-analog-ads1219.mdx)
 - [Input History](../../add-ons/input-history.mdx)
 - [Input Reverse](../../add-ons/input-reverse.mdx)
-- [Joystick Selection Slider](../../add-ons/joystick-selection-slider.mdx)
 - [Keyboard Host Configuration](../../add-ons/keyboard-host.mdx)
 - [On-board LED Configuration](../../add-ons/on-board-led.mdx)
 - [Player Number (X-INPUT ONLY)](../../add-ons/player-number.mdx)