Revert "debugger: prevent running from Tarantool REPL"

This reverts commit ace88542.

That commit disabled repl in tarantool for debugger console session
because debugger console wasn't compatible with Tarantool console,
i.e. this code hang in terminal:

```lua
tarantool> dbg = require 'luadebug'
tarantool> dbg()
```

With the previous patch in the patchset, full readline support and
console compatibility was introduced. Thus, no need to disable repl.

Part of #7738

NO_TEST=internal
NO_DOC=internal, revert unpublished
NO_CHANGELOG=internal