[AutoDiff] Fix @differentiable-related override matching crash. (swiftlang#29985)

Remove meaningless `assert(false)` assertion from
`hasOverridingDifferentiableAttribute` in `TypeCheckDeclOverride.cpp`.

The assertion served no purpose and can safely be removed.

Resolves TF-1167. Add test.

Author: dan-zheng

lib/Sema/TypeCheckDeclOverride.cpp

@@ -689,9 +689,6 @@ static bool hasOverridingDifferentiableAttribute(ValueDecl *derivedDecl,
         overrides = false;
         break;
       }
-      if (!derivedParameters && !baseParameters) {
-        assert(false);
-      }
     }
     if (overrides)
       return true;

test/AutoDiff/compiler_crashers_fixed/tf1167-differentiable-attr-override-match.swift

@@ -0,0 +1,24 @@
+// RUN: %target-swift-frontend -enable-experimental-differentiable-programming -typecheck -verify %s
+// REQUIRES: asserts
+
+// TF-1167: `OverrideMatcher::match` crash due to meaningless assertion:
+// `assert(false)`. The assertion was triggered when parameter indices
+// could not be resolved for neither base nor derived declaration
+// `@differentiable` attributes.
+//
+// `import _Differentiation` is intentionally omitted from this test case.
+
+public protocol Base {
+  associatedtype Input
+  // expected-error @+1 {{use of undeclared type 'Differentiable'}}
+  associatedtype Output: Differentiable
+
+  // expected-error @+1 {{@differentiable attribute used without importing module '_Differentiation'}}
+  @differentiable(wrt: self)
+  func callAsFunction(_ input: Input) -> Output
+}
+public protocol Derived: Base {
+  // expected-error @+1 {{@differentiable attribute used without importing module '_Differentiation'}}
+  @differentiable
+  func callAsFunction(_ input: Input) -> Output
+}