remove to_bool gem

[Azdaroth]

License finder reported one more issue besides colorize - that to_bool has undefined license (which is odd as it clearly has MIT license, but apparently something is off with the gem's metadata). Seems like the best solution was to drop the gem and just implement a simple utility function:

• it's inline with the direction mentioned here about reducing number of dependencies: Reduce the number of 3rd party dependencies #588
• solves license issues
• removes monkeypatch that to_bool introduces for all objects

[andreibondarev]

@Azdaroth Looks good!