Minor adjustment of shebang lines in preprocessing scripts.

Test/VeriFast/tasks/vTaskSwitchContext/preprocessing_scripts/prepare_file_for_VeriFast.sh

@@ -1,5 +1,4 @@
-#!/bin/zsh
-ps -o comm= -p $$
+#!/bin/bash
 
 # This script expects the following command line arguments:
 # $1 : Absolute path to the source file that should be prepared for VeriFast.

Test/VeriFast/tasks/vTaskSwitchContext/preprocessing_scripts/vf_rewrite.sh

@@ -1,4 +1,4 @@
-ps -o comm= -p $$
+#!/bin/bash
 
 # This script rewrites a given source in-pace such that the result can be
 # processed by VeriFast. Each rewrite below concerns a specific construct