Remove minimum pair validation for deploy targets in RPC

[Warashi]

What this PR does:

as title

Why we need it:

We have to continue supporting application registration with a non-plugin-architectured piped.
Such a piped doesn't support deploy targets configuration, so we cannot validate that it must be present.

Which issue(s) this PR fixes:

Part of #5252

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 26.27%. Comparing base (acde5ae) to head (8d88062).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5591      +/-   ##
==========================================
- Coverage   26.28%   26.27%   -0.02%     
==========================================
  Files         470      470              
  Lines       50353    50353              
==========================================
- Hits        13234    13228       -6     
- Misses      36059    36065       +6     
  Partials     1060     1060              

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[t-kikuc]

Thank you!

In the future, it might be better to create AddApplicationRequestV1 if the validation is complex.

[ffjlabo]

LGTM