On verifier failure, don't print a pointer to the File. (#7915)

If the verifier fails, we tried to dump the SemIR::File, but
accidentally dumped a pointer to it instead. However, the raw file dump
is huge and unwieldy, and I don't think it's really helpful, so instead
of including it here, we now just omit the pointer.

toolchain/check/context.cpp

@@ -79,8 +79,7 @@ auto Context::VerifyOnFinish() const -> void {
 
 #ifndef NDEBUG
   if (auto verify = sem_ir_->Verify(); !verify.ok()) {
-    CARBON_FATAL("{0}Built invalid semantics IR: {1}\n", sem_ir_,
-                 verify.error());
+    CARBON_FATAL("Built invalid SemIR: {1}\n", verify.error());
   }
 #endif
 }