fix: remove deprecated comment from RemovePolicy method

[gszw90]

This PR fixes an incorrect deprecation comment in the RemovePolicy method.
The current comment states:

// RemovePolicy removes a policy rule from the model.
// Deprecated: Using AddPoliciesWithAffected instead.
func (model Model) RemovePolicy(sec string, ptype string, rule []string) (bool, error) {
	...
}

However, this is incorrect because:

1. RemovePolicy is used to remove a single policy rule
2. AddPoliciesWithAffected is used to add policy rules
3. These functions have completely different purposes - one removes while the other adds

The deprecation comment has been removed as it was providing incorrect guidance to users of the API.
Note: This issue exists in both v2 and v3 versions of the library.

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Pull request overview

This PR corrects an incorrect deprecation comment on the RemovePolicy method that was mistakenly suggesting users should use AddPoliciesWithAffected instead. The removal is appropriate since:

• RemovePolicy removes a single policy rule
• AddPoliciesWithAffected adds multiple policy rules
• These methods serve opposite purposes (remove vs. add)

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