RISC-V: Remove support for non-existing 'Zve32d'

Since this "extension" does not exist (on the other hand, 'Zve64d' exists)
and it's not useful if we keep it (as other code portions just ignore
"zve32d"), this commit just removes it.

bfd/ChangeLog:

	* elfxx-riscv.c (riscv_supported_std_z_ext): Remove 'Zve32d'
	extension from the list.

bfd/elfxx-riscv.c

@@ -1284,7 +1284,6 @@ static struct riscv_supported_ext riscv_supported_std_z_ext[] =
   {"zkt",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {"zve32x",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {"zve32f",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
-  {"zve32d",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {"zve64x",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {"zve64f",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },
   {"zve64d",		ISA_SPEC_CLASS_DRAFT,		1, 0,  0 },