dtrace/profile: Stop storing the probe name in struct profile_probe

It's unused, and the naked strcpy() was susceptible to buffer overflow
if one creates, say, a probe called "profile-2000000000ns".

Reported by: CHERI
MFC after: 1 week
Sponsored by: Innovate UK

(cherry picked from commit 98ef590f77392159938d2e6f9fd45bf31d10b9c1)