Revert `bootstrap_runtime_toolchain_type` changes

Copybara Import from https://github.com/bazelbuild/rules_java/pull/246

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Revert `bootstrap_runtime_toolchain_type` changes (#246)

This reverts the relevant bits from bcc506228f3ac2c6a811c3414329d8727883685e and 30ecf3ff. The minimum supported Bazel version is now 6.4.0 which includes the type in `@bazel_tools`.

Closes #246
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COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_java/pull/246 from bazelbuild:hvd_tests_for_bootclasspath b666dc289edac950f006b81452193a4dcc91592a
PiperOrigin-RevId: 702260069
Change-Id: Ie64994873a7b5609d4fb8b12a2472c82eb71493b
diff --git a/toolchains/BUILD b/toolchains/BUILD
index ffbffc4..e7f4d84 100644
--- a/toolchains/BUILD
+++ b/toolchains/BUILD
@@ -67,8 +67,8 @@
 #
 # Toolchains of this type are only consumed internally by the bootclasspath rule and should not be
 # accessed from Starlark.
-
-toolchain_type(name = "bootstrap_runtime_toolchain_type")
+# TODO: migrate away from using @bazel_tools//tools/jdk:bootstrap_runtime_toolchain_type ?
+# toolchain_type(name = "bootstrap_runtime_toolchain_type")
 
 # Points to toolchain[":runtime_toolchain_type"] (was :legacy_current_java_runtime)
 java_runtime_alias(name = "current_java_runtime")