Label /system/bin/linker* symlinks as system_file.

Fixes:
avc: denied { read } for comm="init" name="linker_asan64" dev="sda22" ino=1833
scontext=u:r:init:s0 tcontext=u:object_r:system_linker_exec:s0 tclass=lnk_file
permissive=0

Bug: 116486312
Test: adb unroot && adb shell ls -l /system/bin/linker_asan
Change-Id: I754daaf3576e83d516cc9189b8be04dcc41bbc5c

private/file_contexts

@@ -251,7 +251,7 @@
 /system/bin/dnsmasq     u:object_r:dnsmasq_exec:s0
 /system/bin/healthd     u:object_r:healthd_exec:s0
 /system/bin/clatd	u:object_r:clatd_exec:s0
-/system/bin/linker(_asan)?(64)? u:object_r:system_linker_exec:s0
+/system/bin/linker(64)? u:object_r:system_linker_exec:s0
 /system/bin/llkd        u:object_r:llkd_exec:s0
 /system/bin/lmkd        u:object_r:lmkd_exec:s0
 /system/bin/usbd   u:object_r:usbd_exec:s0