build: more compilation flags cleanup

[nerzhul]

• Replaced remaining #ifndef trhing #define thing #end
• Drop 2 irrlicht internal compilation flags which are enabled unconditionally
• remove some useless #IRR_COMPILE checks on android

[nerzhul]

note: current failing jobs are already failing on master branch See: https://github.com/minetest/irrlicht/actions/runs/6411693370/job/17407654243

[numberZero]

note: current failing jobs are already failing on master branch

This is what #250 is ought to fix

[nerzhul]

rebased

[sfan5]

Merged w/ squash