Revert "gnu: %boot3-inputs: Add missing input."

This reverts commit ed2ca2dcb5.

This is no longer needed after the gcc STARTFILE_PREFIX_SPEC commit.

gnu/packages/commencement.scm

@@ -3579,9 +3579,6 @@ (define gcc-final
 (define (%boot3-inputs)
   ;; 4th stage inputs.
   `(("gcc" ,gcc-final)
-    ,@(if (target-riscv64?)
-        `(("gcc:lib" ,gcc-final "lib"))
-        '())
     ("ld-wrapper" ,ld-wrapper-boot3)
     ,@(alist-delete "gcc" (%boot2-inputs))))