Simplify non-optimal points removal.

Summary:
This version is more concise and doesn't need a new scope to reduce visibility of local variable `i`.

Created from CodeHub with https://fburl.com/edit-in-codehub

Reviewed By: mdouze

Differential Revision: D46431189

fbshipit-source-id: 5bbe8df6014d8e25aeb8d5d15145b703e9651327

Author: ttsugriy

faiss/AutoTune.cpp

@@ -152,12 +152,10 @@ bool OperatingPoints::add(
             return false;
         }
     }
-    { // remove non-optimal points from array
-        int i = a.size() - 1;
-        while (i > 0) {
-            if (a[i].t < a[i - 1].t)
-                a.erase(a.begin() + (i - 1));
-            i--;
+    // remove non-optimal points from array
+    for (int i = a.size() - 1; i > 0; --i) {
+        if (a[i].t < a[i - 1].t) {
+            a.erase(a.begin() + (i - 1));
         }
     }
     return true;