Drop wrong comment in docstring

I believe, there is only two solutions.  Here is also
Mathematica's 7 output:

```
    In[1]:= Solve[-x^(1/5) + x^(1/3) + 1/7 == 0, x]

    Out[1]= {{x ->
       Root[1 - 48706 #1 + 1367434327 #1^2 - 2107426771968 #1^3 +
          10242552528740 #1^4 + 4747561509943 #1^5 &, 2]}, {x ->
       Root[1 - 48706 #1 + 1367434327 #1^2 - 2107426771968 #1^3 +
          10242552528740 #1^4 + 4747561509943 #1^5 &, 3]}}
```

diofant/solvers/solvers.py

@@ -629,7 +629,7 @@ def solve(f, *symbols, **flags):
 
         >>> from diofant import real_root, Rational
         >>> eq = root(x, 3) - root(x, 5) + Rational(1, 7)
-        >>> solve(eq)  # this gives 2 solutions but misses a 3rd
+        >>> solve(eq)
         [RootOf(7*_p**5 - 7*_p**3 + 1, _p, 1)**15,
          RootOf(7*_p**5 - 7*_p**3 + 1, _p, 2)**15]
         >>> sol = solve(eq, check=False)