feat: Change symmath to xmodule

scripts/post-pip-compile.sh uses common/lib/symmath/ as its sample
directory to clean up after using pip-tools. Since symmath has been
removed, xmodule, the largest of the directories in common/lib/ will
replace it.

scripts/post-pip-compile.sh

@@ -17,7 +17,7 @@ function clean_file {
     # Workaround for https://github.com/jazzband/pip-tools/issues/204 -
     # change absolute paths for local editable packages back to relative ones
     FILE_CONTENT=$(<${FILE_PATH})
-    FILE_URL_REGEX="-e (file:///[^"$'\n'"]*)/common/lib/symmath"
+    FILE_URL_REGEX="-e (file:///[^"$'\n'"]*)/common/lib/xmodule"
     if [[ "${FILE_CONTENT}" =~ ${FILE_URL_REGEX} ]]; then
         BASE_FILE_URL=${BASH_REMATCH[1]}
         sed "s|$BASE_FILE_URL/||" ${FILE_PATH} > ${TEMP_FILE}