kconfig: remove silentoldconfig target

As commit 911a91c ("kconfig: rename silentoldconfig to
syncconfig") announced, it is time for the removal.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

Documentation/networking/ice.rst

@@ -20,7 +20,7 @@ Enabling the driver
 The driver is enabled via the standard kernel configuration system,
 using the make command::
 
-  make oldconfig/silentoldconfig/menuconfig/etc.
+  make oldconfig/menuconfig/etc.
 
 The driver is located in the menu structure at:
 

scripts/kconfig/Makefile

@@ -68,14 +68,7 @@ PHONY += $(simple-targets)
 $(simple-targets): $(obj)/conf
 	$< $(silent) --$@ $(Kconfig)
 
-PHONY += silentoldconfig savedefconfig defconfig
-
-# We do not expect manual invokcation of "silentoldcofig" (or "syncconfig").
-silentoldconfig: syncconfig
-	@echo "  WARNING: \"silentoldconfig\" has been renamed to \"syncconfig\""
-	@echo "            and is now an internal implementation detail."
-	@echo "            What you want is probably \"oldconfig\"."
-	@echo "            \"silentoldconfig\" will be removed after Linux 4.19"
+PHONY += savedefconfig defconfig
 
 savedefconfig: $(obj)/conf
 	$< $(silent) --$@=defconfig $(Kconfig)