chore(ios): remove dead Swift-side keyboard gesture code

[jahorton]

This PR removes what is essentially dead code.

While working on a different PR this sprint, I remembered that way back in the past, with #2959, we changed the iOS keyboard engine to use the Web-based subkey menu. At the time, we hoped that what we saw as a bug would be fixed and that we'd be able to reverse the decision. A lot has changed since then, and we're now fully committed to handling all keyboard gestures fully on the JS side, within the WebView... so there's no longer any real reason to keep this code around.

Note that the Swift-side gesture handlers actually are still connected... but the functionality they exist to facilitate never utilizes them.

I originally thought this might be related to #11650, but it turned out to have a different underlying cause. Still... being able to delete over 800 lines of code is pretty significant.

User Testing

TEST_GENERAL_USE: do some general testing of the Keyman app for iOS and its system keyboard; things should work the same as usual.

[keymanapp-test-bot]

User Test Results

Test specification and instructions

• ✅ TEST_GENERAL_USE (PASSED): I tested this issue with the attached "Keyman 18.0.48-alpha-test-11672" build on an iOS mobile(physical device) environment: Here is my observation. (notes)

Test Artifacts

• iOS
  • Keyman for iOS (simulator image)
  • FirstVoices Keyboards for iOS (simulator image)
  • TestFlight internal PR build version - 18.0.48 (0.11672.11181)

[dinakaranr]

Test Results

• TEST_GENERAL_USE (PASSED): I tested this issue with the attached "Keyman 18.0.48-alpha-test-11672" build on an iOS mobile(physical device) environment: Here is my observation.

1. Installed the "Keyman 18.0.47.apk" file and gave all permissions to the application.
2. Checked the "Enable Keyman as system-wide keyboard" and set the keyboard as the default keyboard box on the settings page.
3. Open the Keyman app.
4. Used various gesture features( "long press,"  "flick," and "multitap")

I tested the gesture features, such as "long press,"  "flick," and "multitap". I can hold the key and select a letter from the submenu. Caplock is enabled after pressing the "shift" key multiple times. "Long press" and "Multitap" are working fine. Flick is working when you slide down the key. It works well. Thank you.

[keyman-server]

Changes in this pull request will be available for download in Keyman version 18.0.51-alpha