Don't use separate variable for number of trinkets in level

Same principle as removing the separate variable to track number of
collected trinkets. This means it's less error-prone as we're no longer
tracking number of trinkets separately.

In the function that counts the number of trinkets, I would've liked to
have used std::count_if(). However, the most optimal way would require
using a lambda, and lambdas are too new for the C++ standard we're
using. So I just bit the bullet and counted them manually.

desktop_version/src/Script.cpp

@@ -1890,7 +1890,7 @@ void scriptclass::run()
 #if !defined(NO_CUSTOM_LEVELS)
 				if (map.custommode)
 				{
-					usethisnum = help.number(ed.numtrinkets);
+					usethisnum = help.number(ed.numtrinkets());
 				}
 				else
 #endif