docs: ThreadGetMyExternalIP has been removed

It was removed in https://github.com/bitcoin/bitcoin/pull/5161
Remove misleading comment about testnet's message string.
Merge pull request #5348

be4ac91 docs: ThreadGetMyExternalIP has been removed (Pavel Vasin)
Merge pull request #5350

e0535e1 Remove misleading comment about testnet's message string. (Pavel Janík)
Prioritize and display -testsafemode status in UI

Like in a real world situation, a safe mode test should also be visible in the
UI. A test of safe mode is furthermore mostly relevant for developers, so it
should not be overwritten by a warning about a pre-release test build.
Merge pull request #5356

7357893 Prioritize and display -testsafemode status in UI (dexX7)