Remove header_compiler_direct_opts from java_toolchain (#379)

java_tools v21.0 bundles protobuf 36.0, whose Java runtime no longer uses sun.misc.Unsafe for standard generated code. That removes the JDK 24+ warning that motivated header_compiler_direct_opts as a TurbineDirect workaround.

Drop the attribute before it becomes API surface. The direct header compiler no longer needs --sun-misc-unsafe-memory-access=allow for protobuf. A native turbine_direct_graal would also treat JVM flags passed through this attribute as Turbine command-line options.

Fixes #374

RELNOTES: None

Closes #379

COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_java/pull/379 from davido:revert-header-compiler-direct-opts eec72e458f6804ed52a699a92f82a5d52aca0693
PiperOrigin-RevId: 970407219
Change-Id: I30b00796fd175de88d05477fe9cc67a3cce5a2c7

java/common/rules/java_toolchain.bzl

diff --git a/java/common/rules/java_toolchain.bzl b/java/common/rules/java_toolchain.bzl
index a635c5d..a24ae4f 100644
--- a/java/common/rules/java_toolchain.bzl
+++ b/java/common/rules/java_toolchain.bzl
@@ -91,9 +91,6 @@
     else:
         header_compiler_direct_data = []
         header_compiler_direct_jvm_opts = []
-
-    header_compiler_direct_jvm_opts = header_compiler_direct_jvm_opts + ctx.attr.header_compiler_direct_opts
-
     if ctx.attr.oneversion_allowlist and ctx.attr.oneversion_whitelist:
         fail("oneversion_allowlist and oneversion_whitelist are mutually exclusive")
     oneversion_allowlist = ctx.file.oneversion_allowlist if ctx.file.oneversion_allowlist else ctx.file.oneversion_whitelist
@@ -591,18 +588,6 @@
 The list of arguments for the JVM when invoking turbine.
             """,
         ),
-        "header_compiler_direct_opts": attr.string_list(
-            doc = """
-Additional options passed to the direct header compiler, verbatim and without
-location or make-variable expansion.
-
-Warning: these are only meaningful when the direct header compiler runs on a
-JVM, such as TurbineDirect's deploy jar. A native direct header compiler such
-as turbine_direct_graal parses them as Turbine command-line options, so do not
-set JVM options (for example --sun-misc-unsafe-memory-access=allow) when a
-native direct header compiler is in use.
-            """,
-        ),
         "xlint": attr.string_list(
             default = [],
             doc = """