tests/functional/lang: Remove disabled tail-call test

It was introduced back in 2013, was disabled in 2014 again for dubious
reasons and according to horrors is unsound anyways and can never really
work.

It was the only disabled test, so I removed the "infrastructure" for
that in the test runner as well. functional2/lang will have much better
ways for skipping tests anyways

Change-Id: Icb8697fb85221e3206fb64cb917c03607ef278a7

tests/functional/lang.sh

@@ -117,7 +117,7 @@ for i in eval-okay-*.nix; do
             echo "FAIL: $i should evaluate"
             badExitCode=1
         fi
-    elif test ! -e "$i.exp-disabled"; then
+    else
         if
             expect 0 env \
                 NIX_PATH=dir3:dir4 \

tests/functional/lang/eval-okay-tail-call-1.exp-disabled

@@ -1 +0,0 @@
-100000

tests/functional/lang/eval-okay-tail-call-1.nix

@@ -1,3 +0,0 @@
-let
-  f = n: if n == 100000 then n else f (n + 1);
-in f 0