Remove mention of obsolete input_methods.txt in a test comment.

input_methods.txt [1] is the legacy config file from before the
migration to extension-based input methods circa 2011. Almost all of
its contents are obsolete and should no longer be used for reference.

[1] https://source.chromium.org/chromium/chromium/src/+/master:chromeos/ime/input_methods.txt;drc=8cbe6597e4cc8457f4e33ef2ad189f0553f59f54

Bug: 1134526
Change-Id: I4d6023e396b7e44eda47882a33dd093ed10e5dca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2576993
Commit-Queue: Bao-Duy Tran <tranbaoduy@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Auto-Submit: Bao-Duy Tran <tranbaoduy@chromium.org>
Reviewed-by: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834577}

chrome/browser/chromeos/input_method/input_method_manager_impl_unittest.cc

@@ -808,7 +808,6 @@ TEST_F(InputMethodManagerImplTest, TestXkbSetting) {
   EXPECT_TRUE(manager_->GetActiveIMEState()->ReplaceEnabledInputMethods(ids));
   EXPECT_EQ(4U, manager_->GetActiveIMEState()->GetNumActiveInputMethods());
   EXPECT_EQ(2, keyboard_->set_current_keyboard_layout_by_name_count_);
-  // See input_methods.txt for an expected XKB layout name.
   EXPECT_EQ("us(dvorak)", keyboard_->last_layout_);
   manager_->GetActiveIMEState()->SwitchToNextInputMethod();
   EXPECT_EQ(3, keyboard_->set_current_keyboard_layout_by_name_count_);