Lmod installation broken due to Lua+Prefix issues

[bedroge]

In #98 I noticed that the action for testing the Prefix installation playbook was failing, and this is (again) due to Lua stuff not installing correctly inside Gentoo Prefix.

It looks like they added a fix for luaposix, which requires us to revert a change in our eclass/lua-utils.eclass (which was taken from here and: https://bugs.gentoo.org/768909):

			LUA_INCLUDE_DIR)
				local val

				val=$($(tc-getPKG_CONFIG) --variable includedir ${impl}) || die
                                # ADD THE FOLLOWING LINE:
                                val="${val#${ESYSROOT#${SYSROOT}}}"

				export LUA_INCLUDE_DIR=${val}
				debug-print "${FUNCNAME}: LUA_INCLUDE_DIR = ${LUA_INCLUDE_DIR}"

But then dev-lua/lpeg breaks, for which I opened a PR here:
gentoo/gentoo#20576

So if this gets merged, we can add the change to the eclass file, and remove our custom luaposix ebuild.

[bedroge]

Both issues have been fixed in the gentoo overlay.