Clean up enrollment directory

Signed-off-by: João Victor Tozatti Risso <jvtr12@inf.ufpr.br>

src/libs/enrollment/common.js

-const libs = `${process.cwd()}/libs`;
-
-const log = require(`${libs}/log`)(module);
-
-const sqlDecorator = require(`${libs}/query_decorator`);
-
-const yearRange = () => {
-    const yearSql = 'SELECT MIN(t.ano_censo) AS start_year, MAX(t.ano_censo)'
-        + 'AS end_year FROM turmas AS t';
-    log.debug('Generated SQL query for enrollments\' year range');
-    return sqlDecorator.execQuery(yearSql, []);
-};
-
-module.exports = yearRange;