[vscode] builtin terminal-suggest depends on proposed APIs not available

[rschnekenbu]

The vscode builtin 'terminal-suggest' relies on several proposed APIs not implemented yet in theia:

• "terminalCompletionProvider",
• "terminalShellEnv",
• "terminalShellType"

As there are no plans to implement those proposed APIs currently, this builtin shall be removed from the list of available builtins in the Theia project.