chore(plugin.md) - Remove find and search commands from man pages

[dcarrot2]

PR Checklist

• [x ] The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• [ x] There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• [ x] You have signed the CLA.
• [ x] All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

tns plugin -h contains deprecated plugin commands find and search. This removes the commands from the help prompt.

What is the new behavior?

See above.

Fixes #3834 .

[rosen-vladimirov]

Hey @dcarrot2 ,
Thanks for the contribution!