Revert "Add FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION to fuzzer mode and enable DCHECKs under fuzzing (#5489)" (#5580)

This reverts commit 1889ee3904.

We have identified that this is causing ODR violations, because the
`fuzzer` feature is being added `cc_fuzz_test` targets, and thus any
includes they make, but not to the rest of the build. Any include that
is seen from both places has ODR violations if it branches on
FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION.

We need to apply fuzzer globally when building fuzz targets somehow, or
not set different defines in fuzzer.

bazel/cc_toolchains/clang_cc_toolchain_config.bzl

@@ -661,20 +661,12 @@ def _impl(ctx):
 
     fuzzer = feature(
         name = "fuzzer",
-        flag_sets = [
-            flag_set(
-                actions = all_compile_actions + all_link_actions,
-                flag_groups = [flag_group(flags = [
-                    "-fsanitize=fuzzer-no-link",
-                ])],
-            ),
-            flag_set(
-                actions = all_compile_actions,
-                flag_groups = [flag_group(flags = [
-                    "-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION",
-                ])],
-            ),
-        ],
+        flag_sets = [flag_set(
+            actions = all_compile_actions + all_link_actions,
+            flag_groups = [flag_group(flags = [
+                "-fsanitize=fuzzer-no-link",
+            ])],
+        )],
     )
 
     # Clang HARDENED_MODE has 4 possible values: