Remove armhf templates and move to multi-arch / buildx

Migrate as per the python3 template in the classic Go
templates, where a separate -armhf/-arm64 template is not
required and TARGETPLATFORM is introduced for use with
buildkit / buildx and faas-cli publish.

Tested with an RPi with a 32-bit OS and with a 64-bit ARM
OS (Ubuntu 20.04).

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

Author: alexellis

README.md

@@ -5,17 +5,16 @@ The Python Flask templates that make use of the incubator project [of-watchdog](
 
 Templates available in this repository:
 
-- python27-flask
+- python3-http
+- python3-http-debian (ideal for compiled dependencies like numpy, pandas, pillow)
+
 - python3-flask
-- python3-flask-debian
-- python3-flask-armhf
+- python3-flask-debian (ideal for compiled dependencies like numpy, pandas, pillow)
 
-- python3-http
-- python3-http-debian
-- python3-http-armhf
+- python27-flask (Python 2.7 is deprecated)
 
 Notes:
-- To build and deploy a function for Raspberry Pi or ARMv7 in general, use the language templates ending in *-armhf*
+- To build and deploy a function for an ARM computer, you'll need to use `faas-cli publish --platforms`
 
 ## Picking your template