remove c#7 features for compatibility with 2015 Build Tools
remove c#7 features for compatibility with 2015 Build Tools

https://github.com/godotengine/godot/issues/15742
godotengine/godot,Faless/godot,sanikoyes/godot,godotengine/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,honix/godot,Faless/godot,Valentactive/godot,vkbsb/godot,Paulloz/godot,guilhermefelipecgs/godot,akien-mga/godot,honix/godot,akien-mga/godot,guilhermefelipecgs/godot,RandomShaper/godot,ex/godot,Paulloz/godot,godotengine/godot,ex/godot,Valentactive/godot,firefly2442/godot,okamstudio/godot,groud/godot,Zylann/godot,MarianoGnu/godot,Valentactive/godot,RandomShaper/godot,MarianoGnu/godot,RandomShaper/godot,MarianoGnu/godot,guilhermefelipecgs/godot,guilhermefelipecgs/godot,honix/godot,BastiaanOlij/godot,Zylann/godot,DmitriySalnikov/godot,mcanders/godot,ex/godot,sanikoyes/godot,RandomShaper/godot,ZuBsPaCe/godot,ZuBsPaCe/godot,okamstudio/godot,vnen/godot,Zylann/godot,Zylann/godot,RandomShaper/godot,mcanders/godot,mcanders/godot,NateWardawg/godot,DmitriySalnikov/godot,sanikoyes/godot,Shockblast/godot,pkowal1982/godot,MarianoGnu/godot,Valentactive/godot,DmitriySalnikov/godot,DmitriySalnikov/godot,Paulloz/godot,okamstudio/godot,pkowal1982/godot,Faless/godot,NateWardawg/godot,vnen/godot,BastiaanOlij/godot,josempans/godot,Zylann/godot,godotengine/godot,vnen/godot,Shockblast/godot,sanikoyes/godot,Faless/godot,josempans/godot,guilhermefelipecgs/godot,akien-mga/godot,josempans/godot,Valentactive/godot,akien-mga/godot,NateWardawg/godot,BastiaanOlij/godot,mcanders/godot,NateWardawg/godot,pkowal1982/godot,ex/godot,akien-mga/godot,ZuBsPaCe/godot,Valentactive/godot,akien-mga/godot,firefly2442/godot,sanikoyes/godot,ZuBsPaCe/godot,sanikoyes/godot,josempans/godot,vnen/godot,Shockblast/godot,sanikoyes/godot,vnen/godot,okamstudio/godot,firefly2442/godot,BastiaanOlij/godot,akien-mga/godot,vkbsb/godot,groud/godot,BastiaanOlij/godot,ZuBsPaCe/godot,godotengine/godot,mcanders/godot,Shockblast/godot,NateWardawg/godot,BastiaanOlij/godot,pkowal1982/godot,vnen/godot,Faless/godot,Faless/godot,guilhermefelipecgs/godot,josempans/godot,DmitriySalnikov/godot,vkbsb/godot,okamstudio/godot,josempans/godot,Shockblast/godot,groud/godot,BastiaanOlij/godot,firefly2442/godot,Paulloz/godot,firefly2442/godot,BastiaanOlij/godot,mcanders/godot,Paulloz/godot,honix/godot,firefly2442/godot,MarianoGnu/godot,MarianoGnu/godot,josempans/godot,ZuBsPaCe/godot,Zylann/godot,pkowal1982/godot,Shockblast/godot,okamstudio/godot,groud/godot,ex/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,ex/godot,godotengine/godot,Faless/godot,vnen/godot,Paulloz/godot,firefly2442/godot,Valentactive/godot,groud/godot,godotengine/godot,pkowal1982/godot,NateWardawg/godot,vkbsb/godot,groud/godot,DmitriySalnikov/godot,vnen/godot,akien-mga/godot,okamstudio/godot,vkbsb/godot,Faless/godot,firefly2442/godot,ex/godot,MarianoGnu/godot,MarianoGnu/godot,honix/godot,Paulloz/godot,vkbsb/godot,Zylann/godot,pkowal1982/godot,ex/godot,NateWardawg/godot,RandomShaper/godot,pkowal1982/godot,Zylann/godot,Shockblast/godot,godotengine/godot,RandomShaper/godot,DmitriySalnikov/godot,vkbsb/godot,okamstudio/godot,sanikoyes/godot,NateWardawg/godot,Shockblast/godot,okamstudio/godot,Valentactive/godot,NateWardawg/godot,vkbsb/godot,honix/godot,okamstudio/godot,josempans/godot