[Jenkins] Don't update LTP submodule twice

Jenkins already runs a recursive submodule update. So no need to do this
again manually.

Jenkinsfiles/Linux

@@ -25,7 +25,6 @@ pipeline {
                             '''
                         sh '''
                             cd LibOS/shim/test/apps/ltp
-                            git submodule update --init src
                             make
                             ./syscalls.sh
                             '''

Jenkinsfiles/Linux-Debug

@@ -23,7 +23,6 @@ pipeline {
                             '''
                         sh '''
                             cd LibOS/shim/test/apps/ltp
-                            git submodule update --init src
                             make
                             ./syscalls.sh
                             '''