Remove outdated LuaJIT 64bit check

Removed an outdated check for LuaJIT 64bit which states that a 64bit
version is not available. This is no longer true as a 64bit version of
LuaJIT is now available.
Merge pull request #434 from admdly/remove-outdated-luajit-check

Remove outdated LuaJIT 64bit check