shell tests: Drop incorrect uses of readonly.

Change-Id: I47daa31aa6c1f996162328cbfa0abf94566aa5cd
diff --git a/test/tools_common.sh b/test/tools_common.sh
index 974d933..c087106 100755
--- a/test/tools_common.sh
+++ b/test/tools_common.sh
@@ -153,10 +153,10 @@
 # included in $tool_paths, or an empty string. Caller is responsible for testing
 # the string once the function returns.
 aom_tool_path() {
-  local readonly tool_name="$1"
-  local readonly root_path="${LIBAOM_BIN_PATH}"
-  local readonly suffix="${AOM_TEST_EXE_SUFFIX}"
-  local readonly tool_paths="\
+  local tool_name="$1"
+  local root_path="${LIBAOM_BIN_PATH}"
+  local suffix="${AOM_TEST_EXE_SUFFIX}"
+  local tool_paths="\
     ${root_path}/${tool_name}${suffix} \
     ${root_path}/../${tool_name}${suffix} \
     ${root_path}/tools/${tool_name}${suffix} \
@@ -338,8 +338,8 @@
 # Do a small encode for testing decoders.
 encode_yuv_raw_input_av1() {
   if [ "$(av1_encode_available)" = "yes" ]; then
-    local readonly output="$1"
-    local readonly encoder="$(aom_tool_path aomenc)"
+    local output="$1"
+    local encoder="$(aom_tool_path aomenc)"
     shift
     eval "${encoder}" $(yuv_raw_input) \
       $(aomenc_encode_test_fast_params) \