Remove duplicate text

Author: MarkBaker

README.md

@@ -57,15 +57,10 @@ together with functions for
  - ln (natural log)
  - log10 (base-10 log)
  - log2 (base-2 log)
- - negative (reverse signs of both real and imaginary values)
 
 ---
 
 Planned additional functionality, but still to implement
 
  * pow (power)
- - haversine (haversine)
- - inversehaversine (inverse haversine)
- - gudermannian (gudermannian)
- - inversegudermannian (inverse gudermannian)