pageserver: remove no-op attempt to report fail/failpoint feature (#4879)

## Problem

The current output from a prod binary at startup is:
```
git-env:765455bca22700e49c053d47f44f58a6df7c321f failpoints: true, features: [] launch_timestamp: 2023-08-02 10:30:35.545217477 UTC
```

It's confusing to read that line, then read the code and think "if
failpoints is true, but not in the features list, what does that mean?".
As far as I can tell, the check of `fail/failpoints` is just always
false because cargo doesn't expose features across crates like this: the
`fail/failpoints` syntax works in the cargo CLI but not from a macro in
some crate other than `fail`.

## Summary of changes

Remove the lines that try to check `fail/failpoints` from the pageserver
entrypoint module. This has no functional impact but makes the code
slightly easier to understand when trying to make sense of the line
printed on startup.

pageserver/src/bin/pageserver.rs

@@ -38,8 +38,6 @@ const PID_FILE_NAME: &str = "pageserver.pid";
 const FEATURES: &[&str] = &[
     #[cfg(feature = "testing")]
     "testing",
-    #[cfg(feature = "fail/failpoints")]
-    "fail/failpoints",
 ];
 
 fn version() -> String {