Remove cycles field from mos6502 struct

It was both unused and not necessary, as we can simply compute the
number of cycles in the execute function.

include/mos6502.h

@@ -54,21 +54,6 @@ typedef struct {
      */
     vm_16bit last_addr;
 
-    /*
-     * This field contains the number of CPU cycles that the last
-     * instruction handled should consume. In order to accurately
-     * emulate any architecture, we must model the type of "wait" time
-     * each instruction would cause.
-     *
-     * It should also be pointed out that the number of cycles is both
-     * informed by the instruction _and_ the address mode. For example,
-     * an instruction executed in zero-page address mode would consume
-     * fewer cycles than one executed in absolute address mode, because
-     * in the latter, the CPU would have to read ahead to discover a
-     * 16-bit operand vs. the 8-bit operand in the former.
-     */
-    int cycles;
-
     /*
      * Our program counter register; this is what we'll use to determine
      * where we're "at" in memory while executing opcodes. We use a

src/mos6502.c

@@ -150,7 +150,6 @@ mos6502_create()
     cpu->memory = vm_segment_create(MOS6502_MEMSIZE);
 
     cpu->last_addr = 0;
-    cpu->cycles = 0;
     cpu->PC = 0;
     cpu->A = 0;
     cpu->X = 0;