remove goFree() (#6808)
remove goFree() (#6808)

__go_free() was removed from gcc-7.2.0 so we stop trying to help the
garbage collector by marking no longer used memory regions
dom96/Nim,russpowers/Nim,russpowers/Nim,dom96/Nim,russpowers/Nim,russpowers/Nim,dom96/Nim,dom96/Nim,dom96/Nim,russpowers/Nim,dom96/Nim,dom96/Nim,russpowers/Nim,russpowers/Nim