chore(iOS): drop stale React-RCTImage DEFINES_MODULE comment

[kkafar]

Stacked on top of #4036. Merge that one first.

Description

Removes the long comment above rnscreens_config['DEFINES_MODULE'] = 'YES'
in RNScreens.podspec. The comment warned that this setting required
patching React-RCTImage to set DEFINES_MODULE, and concluded
"we can not have Swift code in stable package."

That justification no longer applies: the upstream React-RCTImage
DEFINES_MODULE fix shipped in React Native 0.81, and this library's
minimum supported RN version is now >= 0.81. Users no longer need
to patch their react-native sources, so the comment is misleading.

This is split out from #4036 (which flips the gamma default to
opt-out) on purpose: that PR is a behavior change, this one is a
pure comment removal with its own justification.

Changes

• Drop the 6-line comment block in RNScreens.podspec above the
  DEFINES_MODULE assignment.

Test plan

No code change — only a comment removed. Verified locally that
pod install in FabricExample/ios still succeeds with the
default (gamma-enabled) configuration.

Checklist

• Included code example that can be used to test this change.
• For visual changes, included screenshots / GIFs / recordings documenting the change.
• For API changes, updated relevant public types.
• Ensured that CI passes