gas/arc: Remove preprocess_operands function

gas/arc: Remove preprocess_operands function

The preprocess_operands function changes the incoming list of assembler
tokens based on the assumption that the first arc_operand found will be
the same instruction class as all of the arc_operands for the same
mnemonic.

Though this assumption is probably fine, removing this assumption, and
pushing the token change down into assemble_tokens makes the code no
more complex, and might even be easier to follow.

There should be no user visible changes after this commit.

gas/ChangeLog:

	* config/tc-arc.c (find_opcode_match): Handle O_symbol case, add
	new de_fault label.
	(preprocess_operands): Delete.
	(assemble_tokens): Remove call to preprocess_operands.