all.sh: clean up some uses of "local" variables

While pure sh doesn't have a concept of local variables, we can partially
emulate them by unsetting variables before we exit the function, and use the
convention of giving them lowercase names to distinguish from global
variables.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index f2b3463..32efc1d 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -682,11 +682,12 @@
 component_check_test_cases () {
     msg "Check: test case descriptions" # < 1s
     if [ $QUIET -eq 1 ]; then
-        OPT='--quiet'
+        opt='--quiet'
     else
-        OPT=''
+        opt=''
     fi
-    record_status tests/scripts/check-test-cases.py $OPT
+    record_status tests/scripts/check-test-cases.py $opt
+    unset opt
 }
 
 component_check_doxygen_warnings () {
@@ -1942,7 +1943,7 @@
 
     # Restore the build tree to a clean state.
     cleanup
-    current_component=""
+    unset current_component
 }
 
 # Preliminary setup