Remove death tests checking for assertions. (#6202)

Fixes #5800 (flaky test timeouts under -c dbg), which were caused by
these death tests being extremely slow because they cause the symbolizer
to run on a large debug binary. Before this change, the test ran for
~30-90s depending on how long the symbolization happened to take; after
this change, it finishes in about 0.4s.

Using death tests here seems a bit excessive, especially as the process
dying in these cases isn't part of the contract of these functions, so
I'm just removing the death tests rather than trying to make them more
efficient. We have death tests in common/ that check our CARBON_CHECK
macros work.

toolchain/sem_ir/name_scope_test.cpp

@@ -21,7 +21,6 @@ TEST(ScopeLookupResult, MakeWrappedLookupResultUsingExistingInstId) {
   EXPECT_FALSE(result.is_poisoned());
   EXPECT_TRUE(result.is_found());
   EXPECT_EQ(result.target_inst_id(), inst_id);
-  EXPECT_DEATH(result.poisoning_loc_id(), "is_poisoned");
   EXPECT_EQ(result.access_kind(), AccessKind::Protected);
   EXPECT_TRUE(result == result);
 }
@@ -32,8 +31,6 @@ TEST(ScopeLookupResult, MakeWrappedLookupResultUsingNoneInstId) {
 
   EXPECT_FALSE(result.is_poisoned());
   EXPECT_FALSE(result.is_found());
-  EXPECT_DEATH(result.target_inst_id(), "is_found");
-  EXPECT_DEATH(result.poisoning_loc_id(), "is_poisoned");
   EXPECT_EQ(result.access_kind(), AccessKind::Protected);
   EXPECT_TRUE(result == result);
 }
@@ -45,7 +42,6 @@ TEST(ScopeLookupResult, MakeWrappedLookupResultUsingErrorInst) {
   EXPECT_FALSE(result.is_poisoned());
   EXPECT_TRUE(result.is_found());
   EXPECT_EQ(result.target_inst_id(), ErrorInst::InstId);
-  EXPECT_DEATH(result.poisoning_loc_id(), "is_poisoned");
   EXPECT_EQ(result.access_kind(), AccessKind::Private);
   EXPECT_TRUE(result == result);
 }
@@ -57,24 +53,15 @@ TEST(ScopeLookupResult, MakeFoundExisting) {
   EXPECT_FALSE(result.is_poisoned());
   EXPECT_TRUE(result.is_found());
   EXPECT_EQ(result.target_inst_id(), inst_id);
-  EXPECT_DEATH(result.poisoning_loc_id(), "is_poisoned");
   EXPECT_EQ(result.access_kind(), AccessKind::Protected);
   EXPECT_TRUE(result == result);
 }
 
-TEST(ScopeLookupResult, MakeFoundNone) {
-  EXPECT_DEATH(
-      ScopeLookupResult::MakeFound(InstId::None, AccessKind::Protected),
-      "has_value");
-}
-
 TEST(ScopeLookupResult, MakeNotFound) {
   auto result = ScopeLookupResult::MakeNotFound();
 
   EXPECT_FALSE(result.is_poisoned());
   EXPECT_FALSE(result.is_found());
-  EXPECT_DEATH(result.target_inst_id(), "is_found");
-  EXPECT_DEATH(result.poisoning_loc_id(), "is_poisoned");
   EXPECT_EQ(result.access_kind(), AccessKind::Public);
   EXPECT_TRUE(result == result);
 }
@@ -85,7 +72,6 @@ TEST(ScopeLookupResult, MakePoisoned) {
 
   EXPECT_TRUE(result.is_poisoned());
   EXPECT_FALSE(result.is_found());
-  EXPECT_DEATH(result.target_inst_id(), "is_found");
   EXPECT_EQ(result.poisoning_loc_id(), loc_id);
   EXPECT_EQ(result.access_kind(), AccessKind::Public);
   EXPECT_TRUE(result == result);
@@ -97,7 +83,6 @@ TEST(ScopeLookupResult, MakeError) {
   EXPECT_FALSE(result.is_poisoned());
   EXPECT_TRUE(result.is_found());
   EXPECT_EQ(result.target_inst_id(), ErrorInst::InstId);
-  EXPECT_DEATH(result.poisoning_loc_id(), "is_poisoned");
   EXPECT_EQ(result.access_kind(), AccessKind::Public);
   EXPECT_TRUE(result == result);
 }