feat(3p): upgrade sbcl to 2.1.2

sbcl 2.0.9 introduced a new warning:

> minor incompatible change: the compiler signals a warning at
> compile-time when an initform of T, NIL or 0 does not match
> a STANDARD-CLASS slot's declared type.

This broke a few packages, but they all have been fixed upstream in the
meantime and we only need to bump their versions. The culprits are:

* defclass-std which possibly has become unmaintained since the fix
  (december 2020).

* cl-prevalence which also needs one symbol from bt now

* lisp-binary which also includes a new file now

Change-Id: I06bb47a129d5ef912a623315c1281aedd1ceac2a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2934
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: glittershark <grfn@gws.fyi>

third_party/overlays/tvl.nix

@@ -24,8 +24,4 @@ self: super: {
   clang-tools = (super.clang-tools.override {
     llvmPackages = self.llvmPackages_11;
   });
-
-  # Pick an older version of SBCL as the default, to avoid issues with
-  # warnings in newer SBCL.
-  sbcl = super.sbcl_2_0_8;
 }