remove react-native-linear-gradient package

[hawkrives]

Reasoning:

$ npx @rnx-kit/dep-check --set-version 0.69.0
Need to install the following packages:
  @rnx-kit/dep-check
Ok to proceed? (y)
warn Known bad packages are found in 'all-about-olaf':
    react-native-linear-gradient@*: This package is unmaintained and causes significant degradation in app start up time.

Well, that's enough reason for me to want to remove it!

Alternatives:

• expo-linear-gradient: requires that we install the main expo package, which reaches everywhere (even changing the Android and iOS native host files...)

Screenshots:

(to be uploaded)