Fix broken Bearer links in LIFF API docs

[thinandyavin-tech]

Problem\nThe generated LIFF API documentation links each Bearer authorization scheme to ../README.md#Bearer, but that README does not exist at the relative path. Each link returns 404.\n\n## Change\nReplace the four dead links in linebot/v3/liff/docs/Liff.md with inline Bearer text. The generated example already shows how to configure �ccess_token, so the documentation remains clear without linking to a missing page.\n\nFixes #732

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