imgact_elf: Enable sigfastblock for purecap processes

It's not clear why this was ever disabled in the first place in
6ce214d ("Add AT_BSDFLAGS auxv entry."), and this was even
discussed in December 2020 on Slack but nothing came of it. Since there
are no conceptual problems with it and it seems to work just fine let's
enable it.

sys/kern/imgact_elf.c

@@ -238,11 +238,7 @@ SYSCTL_INT(ASLR_NODE_OID, OID_AUTO, shared_page, CTLFLAG_RWTUN,
     __XSTRING(__CONCAT(ELF, __ELF_WORD_SIZE))
     ": enable shared page address randomization");
 
-#ifdef __ELF_CHERI
-static int __elfN(sigfastblock) = 0;
-#else
 static int __elfN(sigfastblock) = 1;
-#endif
 SYSCTL_INT(ELF_NODE_OID, OID_AUTO, sigfastblock,
     CTLFLAG_RWTUN, &__elfN(sigfastblock), 0,
     "enable sigfastblock for new processes");