Revert "compiler: corrections to Conditional lattice"

This reverts commit e1859a1.
I was wrong, and lattices are hard.

Author: vtjnash

base/compiler/typelattice.jl

@@ -126,12 +126,7 @@ function ⊑(@nospecialize(a), @nospecialize(b))
     @assert !isa(b, TypeVar) "invalid lattice item"
     if isa(a, Conditional)
         if isa(b, Conditional)
-            issubconditional(a, b) && return true
-            b = maybe_extract_const_bool(b)
-            if b isa Bool && maybe_extract_const_bool(a) === b
-                return true
-            end
-            return false
+            return issubconditional(a, b)
         elseif isa(b, Const) && isa(b.val, Bool)
             return maybe_extract_const_bool(a) === b.val
         end

base/compiler/typelimits.jl

@@ -299,10 +299,6 @@ function tmerge(@nospecialize(typea), @nospecialize(typeb))
             isa(typeb, MaybeUndef) ? typeb.typ : typeb))
     end
     # type-lattice for Conditional wrapper
-    if isa(typea, Conditional) && isa(typeb, Conditional) && typea.var !== typeb.var
-        widenconditional(typea) isa Const && (typea = widenconditional(typea))
-        widenconditional(typeb) isa Const && (typeb = widenconditional(typeb))
-    end
     if isa(typea, Conditional) && isa(typeb, Const)
         if typeb.val === true
             typeb = Conditional(typea.var, Any, Union{})