fixing some, removing empty links

Author: FoamyGuy

_board/feather_stm32f405_express.md

@@ -9,7 +9,7 @@ board_url:
 board_image: "feather_stm32f405_express.jpg"
 date_added: 2019-09-26
 family: stm
-download_instructions: https://learn.adafruit.com/introducing-the-adafruit-nrf52840-feather/circuitpython
+download_instructions: https://learn.adafruit.com/adafruit-stm32f405-feather-express/circuitpython-setup
 features:
   - Feather-Compatible
   - Battery Charging

_board/gemma_m0.md

@@ -12,7 +12,7 @@ board_image: "gemma_m0.jpg"
 date_added: 2019-03-09
 family: atmel-samd
 bootloader_id: gemma_m0
-download_instructions: https://learn.adafruit.com/introducing-the-adafruit-nrf52840-feather/circuitpython
+download_instructions: https://learn.adafruit.com/adafruit-gemma-m0/circuitpython
 features:
   - Solder-Free Alligator Clip
 ---

_board/gemma_m0_pycon2018.md

@@ -10,7 +10,7 @@ board_image: "gemma_m0_pycon2018.jpg"
 date_added: 2019-04-13
 family: atmel-samd
 bootloader_id: gemma_m0
-download_instructions: https://learn.adafruit.com/introducing-the-adafruit-nrf52840-feather/circuitpython
+download_instructions: https://learn.adafruit.com/adafruit-gemma-m0/circuitpython
 features:
   - Solder-Free Alligator Clip
 ---

_board/matrixportal_m4.md

@@ -11,7 +11,7 @@ board_image: "matrixportal_m4.jpg"
 date_added: 2020-09-16
 family: atmel-samd
 bootloader_id: matrixportal_m4
-download_instructions: https://learn.adafruit.com/adafruit-matrixportal-m4 
+download_instructions: https://learn.adafruit.com/adafruit-matrixportal-m4/install-circuitpython 
 tags:
   - Matrix Portal
 features:

_board/metro_m7_1011.md

@@ -9,7 +9,7 @@ board_url:
 board_image: "metro_m7_1011.jpg"
 date_added: 2020-10-16
 family: mimxrt10xx
-download_instructions: https://learn.adafruit.com/adafruit-metro-m4-express-featuring-atsamd51/circuitpython
+download_instructions: https://learn.adafruit.com/adafruit-metro-m7-with-airlift/install-circuitpython
 features:
   - Wi-Fi
   - STEMMA QT/QWIIC

_board/pirkey_m0.md

@@ -10,7 +10,6 @@ board_image: "pirkey_m0.jpg"
 date_added: 2019-03-11
 family: atmel-samd
 bootloader_id: pirkey
-download_instructions: 
 ---
 
 The pIRkey adds an IR remote receiver to any computer, laptop, tablet...any computer or device with a USB port that can use a keyboard. This little board slides into any USB A port, and shows up as an every-day USB keyboard. The onboard ATSAMD21 microcontroller listens for IR remote signals and converts them to keypresses, mouse movements, or even USB serial output.