Remove dmd-2.063

[the-horo]

dmd-2.063 no longer builds with neither g++ nor clang++ due to some errors:

func.c: In member function ‘virtual void FuncDeclaration::semantic(Scope*)’:
func.c:500:19: error: narrowing conversion of ‘-1’ from ‘int’ to ‘long unsigned int’ [-Wnarrowing]
  500 |             case -1:
      |                   ^
func.c:540:19: error: narrowing conversion of ‘-2’ from ‘int’ to ‘long unsigned int’ [-Wnarrowing]
  540 |             case -2:    // can't determine because of fwd refs
      |                   ^
func.c:629:23: error: narrowing conversion of ‘-1’ from ‘int’ to ‘long unsigned int’ [-Wnarrowing]
  629 |                 case -1:
      |                       ^
func.c:632:23: error: narrowing conversion of ‘-2’ from ‘int’ to ‘long unsigned int’ [-Wnarrowing]
  632 |                 case -2:
      |                       ^

[mleise]

Sad times, a classic version has left us. :)