feat: removed incentives feature flag and decreased IRO MinEpochsPaidOver default value

[keruch]

Description

---

Closes #XXX

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow-up issues.

PR review checkboxes:

I have...

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Targeted PR against the correct branch
• included the correct type prefix in the PR title
• Linked to the GitHub issue with discussion and accepted design
• Targets only one GitHub issue
• Wrote unit and integration tests
• Wrote relevant migration scripts if necessary
• All CI checks have passed
• Added relevant godoc comments
• Updated the scripts for local run, e.g genesis_config_commands.sh if the PR changes parameters
• Add an issue in the e2e-tests repo if necessary

SDK Checklist

• Import/Export Genesis
• Registered Invariants
• Registered Events
• Updated openapi.yaml
• No usage of go map
• No usage of time.Now()
• Used fixed point arithmetic and not float arithmetic
• Avoid panicking in Begin/End block as much as possible
• No unexpected math Overflow
• Used sendCoin and not SendCoins
• Out-of-block compute is bounded
• No serialized ID at the end of store keys
• UInt to byte conversion should use BigEndian

Full security checklist here

---

For Reviewer:

• Confirmed the correct type prefix in the PR title
• Reviewers assigned
• Confirmed all author checklist items have been addressed

---

After reviewer approval:

• In case the PR targets the main branch, PR should not be squash merge in order to keep meaningful git history.
• In case the PR targets a release branch, PR must be rebased.

[VictorTrustyDev]

this flag already on Playground, remove like this won't cause trouble?

[keruch]

it won't in theory. the first 4 fields are unchanged (which are actually used), so there should not be any serialization issues.