Fix minor nits in the mips outline assembly files. (#653)

- Fix the `.file` string for mips64.s.
 - Fix a redundant `.note.GNU-stack` declaration in mips.s

Author: sunfishcode

src/backend/linux_raw/arch/outline/debug/librustix_outline_mips.a

@@ -186,8 +186,6 @@ rustix_syscall6_nr_last:
     .end        rustix_syscall6_nr_last
     .size       rustix_syscall6_nr_last, .-rustix_syscall6_nr_last
 
-    .section .note.GNU-stack,"",@progbits
-
     .section    .text.rustix_syscall7_nr_last,"ax",@progbits
     .p2align    2
     .weak       rustix_syscall7_nr_last

src/backend/linux_raw/arch/outline/debug/librustix_outline_mips64.a

@@ -7,7 +7,7 @@
 # outline.rs takes care of reordering the nr argument to the end for us,
 # so we only need to move nr into v0.
 
-    .file       "mips.s"
+    .file       "mips64.s"
     .section    .mdebug.abi64
     .previous
     .abicalls