Documentation/Kbuild: Remove references to gcc-plugin.sh

gcc-plugin.sh has been removed in commit
1e860048 ("gcc-plugins: simplify GCC plugin-dev capability test").
Signed-off-by: Robert Karszniewicz <r.karszniewicz@phytec.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Documentation/kbuild/gcc-plugins.rst

@@ -47,12 +47,6 @@ Files
 	This is a compatibility header for GCC plugins.
 	It should be always included instead of individual gcc headers.
 
-**$(src)/scripts/gcc-plugin.sh**
-
-	This script checks the availability of the included headers in
-	gcc-common.h and chooses the proper host compiler to build the plugins
-	(gcc-4.7 can be built by either gcc or g++).
-
 **$(src)/scripts/gcc-plugins/gcc-generate-gimple-pass.h,
 $(src)/scripts/gcc-plugins/gcc-generate-ipa-pass.h,
 $(src)/scripts/gcc-plugins/gcc-generate-simple_ipa-pass.h,