8270820: remove unused stiFileTableIndex from SDE.c

Reviewed-by: cjplummer, sspitsyn

Author: MBaesken

src/jdk.jdwp.agent/share/native/libjdwp/SDE.c

@@ -731,10 +731,6 @@ private jboolean isValid(void);
         return -1;
     }
 
-    private int stiFileTableIndex(int sti, int lti) {
-        return fileTableIndex(sti, lineTable[lti].fileId);
-    }
-
     private jboolean isValid(void) {
         return sourceMapIsValid;
     }