Remove CONFIG_EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER

[ownia]

Since commit e346bebbd36b1576a3335331fed61bb48c6d8823 always enable initrd command line loader, we no longer need this config.

Fix IR image build warning: [INFO]: the following symbols were not found in the active configuration:

• CONFIG_EFI_GENERIC_STUB_INITRD_CMDLINE_LOADER