[AArch64] Fix APAS instructions to disassemble to self not to SYS alias (llvm#142211)

`APAS` instructions currently incorrectly disassemble to `SYS` aliases.
Fix this so that they disassemble to the actual `APAS` instruction.

Author: jthackray

llvm/lib/Target/AArch64/AArch64InstrFormats.td

@@ -1817,7 +1817,6 @@ class APASI : SimpleSystemI<0, (ins GPR64:$Xt), "apas", "\t$Xt">, Sched<[]> {
   bits<5> Xt;
   let Inst{20-5} = 0b0111001110000000;
   let Inst{4-0} = Xt;
-  let DecoderNamespace = "APAS";
 }
 
 // Hint instructions that take both a CRm and a 3-bit immediate.

llvm/test/MC/Disassembler/AArch64/armv9.6a-rme-gpc3.txt

@@ -9,10 +9,10 @@
 [0xa3,0x21,0x3e,0xd5]
 [0xa4,0x21,0x1e,0xd5]
 
-# CHECK:      	sys	#6, c7, c0, #0, x0
-# CHECK-NEXT: 	sys	#6, c7, c0, #0, x1
-# CHECK-NEXT: 	sys	#6, c7, c0, #0, x2
-# CHECK-NEXT: 	sys	#6, c7, c0, #0, x17
-# CHECK-NEXT: 	sys	#6, c7, c0, #0, x30
+# CHECK:      	apas x0
+# CHECK-NEXT: 	apas x1
+# CHECK-NEXT: 	apas x2
+# CHECK-NEXT: 	apas x17
+# CHECK-NEXT: 	apas x30
 # CHECK-NEXT: 	mrs	x3, GPCBW_EL3
 # CHECK-NEXT: 	msr	GPCBW_EL3, x4