Remove end of string check that is now redudant.

The addition of some code to avoid valgrind warnings made this code
redundant.

src/core/peg.c

@@ -214,7 +214,7 @@ tail:
             if (text >= s->text_end) return NULL;
             uint32_t word = rule[1 + (text[0] >> 5)];
             uint32_t mask = (uint32_t)1 << (text[0] & 0x1F);
-            return (text < s->text_end && (word & mask))
+            return (word & mask)
                    ? text + 1
                    : NULL;
         }