[opt](runtime filter)disable runtime filter prune for external table by default (#60138)

### What problem does this PR solve?
set runtime_filter_prune_for_external default value to false

Author: englefly

fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java

@@ -1095,7 +1095,7 @@ public static double getHotValueThreshold() {
     public int autoProfileThresholdMs = -1;
 
     @VariableMgr.VarAttr(name = "runtime_filter_prune_for_external", fuzzy = true)
-    public boolean runtimeFilterPruneForExternal = true;
+    public boolean runtimeFilterPruneForExternal = false;
 
     @VariableMgr.VarAttr(name = "runtime_filter_jump_threshold")
     public int runtimeFilterJumpThreshold = 2;
@@ -3540,7 +3540,6 @@ private void setFuzzyForCatalog(Random random) {
 
         // common
         this.enableCountPushDownForExternalTable = random.nextBoolean();
-        this.runtimeFilterPruneForExternal = random.nextBoolean();
     }
 
     public String printFuzzyVariables() {