test: drop hardware-dependent tests from meson test target

test: drop hardware-dependent tests from meson test target

Currently, the tests under test/ require intractions with actual
hardware, which isn't available under CI.

[Additionally, the test() functions are mostly incorrect, as they'll all
just repeat the same test.c test]

This test drops the test() defitinitons, but leaves the executable()s
available for developer use, and adds a comment to indicate what we're
doing.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>