Cleanup feedback related state, old LIFF page and token mechanism

[MrOrz]

• Remove feedback/yes and feedback/no LIFF pages
• Remove LINE bot GraphQL endpoints related to above pages - context query and voteReply mutation
• Remove LIFF <> LINE bot graphql's bearer token mechanism
  • It was introduced in LIFF as token URL param. LIFF forwards the token back in LINE bot GraphQL, so that LINE bot graphql can authenticate user when determining GraphQL context.
  • However, this whole mechanism is replaced by LIFF v2's ID token (or possibly access token if we remove ID token permission). (Disucssed in 2021/4/13)
  • The last place we use such token was in PositiveFeedback and NegativeFeedback LIFF pages.
  • The mechanism can be removed after the aforementioned LIFF pages are removed
• Remove askingReplyFeedback state handler and its related prefix logic

[coveralls]

Pull Request Test Coverage Report for Build 2559819518

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-1.3%) to 85.648%

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Files with Coverage Reduction	New Missed Lines	%
src/graphql/index.js	1	86.96%

Totals
Change from base Build 2559635494:	-1.3%
Covered Lines:	889
Relevant Lines:	1017

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💛 - Coveralls

[MrOrz]

This branch has been deployed to staging LINE bot; everyone can give it a try.