[BUGFIX 60515] - Fix bug when specifying template_source using net.load_template

[stiltzkin10]

What does this PR do?

Remove unsued code block that causes the script to fail. It sets the local variables salt_render and file_exists, neither of them is used later in the code.

The code block uses template_name which is not mandatory if the user specifies template_source. If template_name is not set, the code crashes.

What issues does this PR fix or reference?

Fixes #60515

Previous Behavior

$ sudo salt XXXX net.load_template template_source='ntp server 192.168.1.100' test=true
XXXX:
    The minion function caused an exception: Traceback (most recent call last):
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/metaproxy/proxy.py", line 479, in thread_return
        return_data = minion_instance.executors[fname](
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 149, in __call__
        return self.loader.run(run_func, *args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1232, in run
        return self._last_context.run(self._run_as, _func_or_method, *args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1247, in _run_as
        return _func_or_method(*args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/executors/direct_call.py", line 10, in execute
        return func(*args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 149, in __call__
        return self.loader.run(run_func, *args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1232, in run
        return self._last_context.run(self._run_as, _func_or_method, *args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1247, in _run_as
        return _func_or_method(*args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/utils/napalm.py", line 502, in func_wrapper
        ret = func(*args, **kwargs)
      File "/opt/saltstack/salt/lib/python3.10/site-packages/salt/modules/napalm_network.py", line 1959, in load_template
        salt_render = False
    AttributeError: 'NoneType' object has no attribute 'startswith'

New Behavior

$ sudo salt XXXX net.load_template template_source='ntp server 192.168.1.100' test=true
XXXX:
    ----------
    already_configured:
        False
    comment:
        Configuration discarded.
    diff:
        +ntp server 192.168.1.100
    loaded_config:
    result:
        True

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

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