STDIN redirect disappeared from the tests

[tyuldashev]

Description
During test generation UTBot used to substitute stdin with own construction, now it does not anymore, so tests with user input fail.

To Reproduce
Steps to reproduce the behavior:

1. Open c-examples from UTBotCPP project
2. Generate tests for int simple_getc() function in file input_output.c

Expected behavior
Previously tests looked like this:

TEST(regression, simple_getc_test_1)
{
    char stdin_buf[] = "\"""";
    int utbot_redirect_stdin_status = 0;
    utbot_redirect_stdin(stdin_buf, utbot_redirect_stdin_status);
    if (utbot_redirect_stdin_status != 0) {
        FAIL() << "Unable to redirect stdin.";
    }
    int actual = simple_getc();
    EXPECT_EQ(-1, actual);
}

Actual behavior
Now utbot_redirect_stdin initialization part disappeared and test looks like this:

TEST(regression, simple_getc_test_1)
{
    int actual = simple_getc();
    EXPECT_EQ(9, actual);
}

[tyuldashev]

BTW any chance we could write unit tests to detect such problems in future? That redirection part is inserted [and actually works].