riscv: Remove gate area stubs

Since commit a6c19dfe39 ("arm64,ia64,ppc,s390,sh,tile,um,x86,mm:
remove default gate area"), which predates riscv's inclusion in
Linux by almost three years, the default behavior wrt the gate area
is sane.  Remove riscv's gate area stubs.

Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: linux-riscv@lists.infradead.org
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

arch/riscv/kernel/vdso.c

@@ -92,22 +92,3 @@ const char *arch_vma_name(struct vm_area_struct *vma)
 		return "[vdso]";
 	return NULL;
 }
-
-/*
- * Function stubs to prevent linker errors when AT_SYSINFO_EHDR is defined
- */
-
-int in_gate_area_no_mm(unsigned long addr)
-{
-	return 0;
-}
-
-int in_gate_area(struct mm_struct *mm, unsigned long addr)
-{
-	return 0;
-}
-
-struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
-{
-	return NULL;
-}