examples: remove session-ttl config from template

[amyangfei]

What problem does this PR solve?

Issue link:

ref: pingcap/tiflow#7404

What is changed and how it works?

session-ttl is no longer used in tiflow, and remove it before pingcap/tiflow#7404 got merged is safe since it has a default value.

Code changes

• Has Go code change
• Has CI related scripts change

Check List

Tests

• Unit test
• E2E test
• Stability test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Note for reviewer

[codecov-commenter]

Codecov Report

Base: 5.61% // Head: 5.61% // No change to project coverage 👍

Coverage data is based on head (596886f) compared to base (39e52a4).
Patch has no changes to coverable lines.

Additional details and impacted files

@@          Coverage Diff           @@
##           master     #43   +/-   ##
======================================
  Coverage    5.61%   5.61%           
======================================
  Files          19      19           
  Lines        1905    1905           
======================================
  Hits          107     107           
  Misses       1785    1785           
  Partials       13      13           

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[lichunzhu]

LGTM