Correct icon used in delete button

[seadowg]

Closes #6209

Why is this the best possible solution? Were any other approaches considered?

Nothing to discuss here really! I just replaced the icon.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

Worth checking the icon is correct, but other than that nothing has changed.

Before submitting this PR, please make sure you have:

• added or modified tests for any new or changed behavior
• run ./gradlew connectedAndroidTest (or ./gradlew testLab) and confirmed all checks still pass
• added a comment above any new strings describing it for translators
• added any new strings with date formatting to DateFormatsTest
• verified that any code or assets from external sources are properly credited in comments and/or in the about file.
• verified that any new UI elements use theme colors. UI Components Style guidelines

[srujner]

Tested with Success!
Verified on device with Android 13

Verified cases:

• Issue Delete layer icon is +, should be trashcan #6209 is no longer reproducing;
• Offline layers checked
• Light and Dark mode;
• Rotate the screen, minimize the app

[dbemke]

Tested with Success!
Verified on device with Android 10