cc: remove a spurious check for UID 0

This drops an hardcoded check for the root user-ID before accessing
`/proc/kallsyms`, in order to fix a bug which is preventing proper
kernel symbols resolution by non-root users.

The `/proc/kallsyms` file is generally available to non-privileged
users:
```
> runuser -u nobody -- wc -l /proc/kallsyms

217514 /proc/kallsyms
```

Its content is further controlled by the `CAP_SYSLOG` capability
through `/proc/sys/kernel/kptr_restrict`:
https://man7.org/linux/man-pages/man7/capabilities.7.html

As such, it is better to directly open it and rely on `fopen()`
for privileges checking.

src/cc/bcc_proc.c

@@ -262,10 +262,6 @@ int bcc_procutils_each_ksym(bcc_procutils_ksymcb callback, void *payload) {
  FILE *kallsyms;
  unsigned long long addr;
 
- /* root is needed to list ksym addresses */
- if (geteuid() != 0)
- return -1;
-
  kallsyms = fopen("/proc/kallsyms", "r");
  if (!kallsyms)
  return -1;