399 update deprecated references

[TheDuckCow]

Will contribute to closing #399

This removes the remaining bv28 code references, used previously to distinguish between 2.8+ and 2.7 code. Along with this, this PR also removes all of this now no-longer relevant 2.7 code, and implements some missing tests for spawners which were also affected. Also removes code referencing layers, since this is only a 2.7x concept.

Also move to use the native user_remap function since this is confidently available now, where before we had an intermediate util used for backwards compatibility.

All tests, including the new ones, passing:

-------------------------------------------------------------------------------
bversion   	ran_tests	ran	skips	failed	errors
-------------------------------------------------------------------------------
(3.6.2)   	all_tests	35	2	0	No errors
(4.0.0)   	all_tests	35	2	0	No errors
(3.5.1)   	all_tests	35	2	0	No errors
(3.4.0)   	all_tests	35	2	0	No errors
(3.3.1)   	all_tests	35	2	0	No errors
(3.2.1)   	all_tests	35	2	0	No errors
(3.1.0)   	all_tests	35	2	0	No errors
(3.0.0)   	all_tests	35	2	0	No errors
(2.93.0)   	all_tests	35	2	0	No errors
(2.90.1)   	all_tests	35	2	0	No errors
(2.80.75)   	all_tests	34	3	0	No errors
tests took 167s to run

[TheDuckCow]

Updated the description, ready for review now.

[StandingPadAnimations]

👍

[StandingPadAnimations]

I'll merge this in now