Remove copyright from codegen template

[khanhtc1202]

What this PR does / why we need it:

There is no need to add copyright to the generated code just as other generated code of pipecd

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.39%. Comparing base (9bf5c33) to head (886042a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4931   +/-   ##
=======================================
  Coverage   29.38%   29.39%           
=======================================
  Files         322      322           
  Lines       40852    40852           
=======================================
+ Hits        12006    12010    +4     
+ Misses      27885    27882    -3     
+ Partials      961      960    -1     

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[t-kikuc]

good

[ffjlabo]

🚀