[rand.eng.philox] Harmonize description of sequenced variable

Author: tkoeppe

source/numerics.tex

@@ -3163,7 +3163,7 @@
   $k = 0, \dotsc, n/2 - 1$ is the index in the sequences,
 
   \item
-  $q$ is the index of the round: $q = 0, \dotsc, r - 1$,
+  $q = 0, \dotsc, r - 1$ is the index of the round,
 
   \item
   $\mathit{key}^q_k$ is the $k^\text{th}$ round key for round $q$,