refactor: remove dead code in the assembler.

[Peefy]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

refactor: remove dead code in the assembler.

2. What is the scope of this PR (e.g. component or file name):

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

All integraition grammar tests.

6. Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[coveralls]

Pull Request Test Coverage Report for Build 4807188889

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 31 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-20.8%) to 67.171%

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Files with Coverage Reduction	New Missed Lines	%
compiler_base/session/src/lib.rs	31	50.0%

Totals
Change from base Build 4795695340:	-20.8%
Covered Lines:	29738
Relevant Lines:	44272

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💛 - Coveralls

[zong-zhe]

LGTM