Drop references to deleted explorer fuzzer (#4745)

Follow up to delete that happened in #4731 .

Co-authored-by: Josh L <josh11b@users.noreply.github.com>

explorer/BUILD

@@ -94,13 +94,6 @@ file_test(
     ),
 )
 
-filegroup(
-    name = "carbon_files",
-    srcs = glob(["testdata/**/*.carbon"]),
-    # Files are used for validating fuzzer completeness.
-    visibility = ["//explorer/fuzzing:__pkg__"],
-)
-
 filegroup(
     name = "treesitter_testdata",
     srcs = glob(

explorer/README.md

@@ -133,11 +133,6 @@ To explain this boilerplate:
 -   `bazel run testdata/DIR/FILE.carbon.verbose` -- Runs explorer on the file
     with tracing enabled.
 
-### Updating fuzzer logic after making AST changes
-
-Please refer to
-[Fuzzer documentation](https://github.com/carbon-language/carbon-lang/blob/trunk/explorer/fuzzing/README.md).
-
 ## Explorer's Trace Output
 
 Explorer's Trace Output refers to a detailed record of program phases and their

explorer/parse_and_execute/BUILD

@@ -6,7 +6,6 @@ load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
 
 package(default_visibility = [
     "//explorer:__pkg__",
-    "//explorer/fuzzing:__pkg__",
 ])
 
 cc_library(

explorer/syntax/BUILD

@@ -94,7 +94,6 @@ cc_library(
     # don't spend time linting it.
     tags = ["no-clang-tidy"],
     visibility = [
-        "//explorer/fuzzing:__pkg__",
         "//explorer/parse_and_execute:__pkg__",
     ],
     deps = [