Drop legacy “devices” in favor of SDL2

[numberZero]

SDL2 supports all Minetest target platforms, is robust and well-maintained. It should be used in favor of custom platform-specific code.

“Devices” to replace:

• Android Drop CIrrDeviceAndroid in favor of SDL #175
• Linux Drop CIrrDeviceLinux in favor of SDL #174
• OSX
• Win32

Depends: #137, #167 (for SDL+GLES), likely #158.

[sfan5]

FWIW iOS is not a currently supported target and we don't have a way to build for it.

[numberZero]

Thanks. One device less.