Clean up runtime OS version check

[ichan-mb]

Since we are raising the minimum OS requirement for Andriod to API level 19 (fuse-open/uno#504) and iOS to iOS 11 (fuse-open/uno#476) This will clean up some unnecessary runtime OS version check

This PR contains:

• Changelog
• Documentation
• Tests

[mortend]

Nice clean up! I approve :)

Though, right now I think the beta-3.0 branch might be a better target for changes like this. Planning to make at least one more 2.x release from master and can't be too paranoid about unintended side effects when removing old code, so feeling better about doing clean-ups like this on a major version.

This branch seems straight-forward to rebase on beta-3.0:

# Add upstream remote (just for reference; you have probably done this already)
git remote add upstream https://github.com/fuse-open/fuselibs.git

# Fetch and rebase
git fetch upstream
git rebase upstream/beta-3.0

Sometimes when things don't rebase nicely (many conflicts or messy history/unwanted commits), it's better to rebase manually:

# Create a backup branch just in case
git branch backup -f

# Fetch and reset local branch to base branch
git fetch upstream
git reset --hard upstream/beta-3.0

# Look up wanted commit SHA(s) in log and cherry-pick
git log backup
git cherry-pick dba34f6b0796b930b42e29d14ca1569584a0ce81

# Force push 😎
git push -f

Also need to edit the GitHub PR to set base: beta-3.0 and personally I like to add (beta-3.0) in the title for reference.

[ichan-mb]

Thank you for your detailed steps, and I've made the changes as per your instructions