docs: infrastructure.rst: don't include firmware kernel-doc

docs: infrastructure.rst: don't include firmware kernel-doc

Those are already documented at:

	Documentation/driver-api/firmware/request_firmware.rst

Including it twice is causing lots of warnings:

	./Documentation/driver-api/infrastructure.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/firmware/request_firmware'.
	Declaration is 'request_firmware'.
	./Documentation/driver-api/infrastructure.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/firmware/request_firmware'.
	Declaration is 'firmware_request_nowarn'.
	./Documentation/driver-api/infrastructure.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/firmware/request_firmware'.
	Declaration is 'request_firmware_direct'.
	./Documentation/driver-api/infrastructure.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/firmware/request_firmware'.
	Declaration is 'firmware_request_platform'.
	./Documentation/driver-api/infrastructure.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/firmware/request_firmware'.
	Declaration is 'firmware_request_cache'.
	./Documentation/driver-api/infrastructure.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/firmware/request_firmware'.
	Declaration is 'request_firmware_into_buf'.
	./Documentation/driver-api/infrastructure.rst: WARNING: Duplicate C declaration, also defined in 'driver-api/firmware/request_firmware'.
	Declaration is 'request_firmware_nowait'.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>