fix(tianmu): fix ALTER table DROP primary key is forbidden (#1034)

[adofsauron]

Summary about this PR

Issue Number: close #1034

Tests Check List

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Changelog

• New Feature
• Bug Fix
• Performance Improvement
• Build/Testing/CI/CD
• Documentation
• Not for changelog (changelog entry is not required)

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features

[mergify]

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[codecov]

Codecov Report

Base: 0.00% // Head: 33.74% // Increases project coverage by +33.74% 🎉

Coverage data is based on head (5fdda07) compared to base (7f96549).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 5fdda07 differs from pull request most recent head a9af499. Consider uploading reports for the commit a9af499 to get more accurate results

Additional details and impacted files

@@                 Coverage Diff                  @@
##           stonedb-5.7-dev    #1055       +/-   ##
====================================================
+ Coverage                 0   33.74%   +33.74%     
====================================================
  Files                    0     1807     +1807     
  Lines                    0   394961   +394961     
====================================================
+ Hits                     0   133277   +133277     
- Misses                   0   261684   +261684     

Impacted Files	Coverage Δ
storage/tianmu/handler/ha_tianmu.cpp	54.89% <100.00%> (ø)
storage/myisam/mi_delete_table.c	53.84% <0.00%> (ø)
sql/net_serv.cc	55.01% <0.00%> (ø)
mysys/mf_wcomp.c	43.33% <0.00%> (ø)
storage/innobase/include/trx0rec.ic	100.00% <0.00%> (ø)
storage/tianmu/base/core/scollectd.cpp	0.00% <0.00%> (ø)
include/mutex_lock.h	75.00% <0.00%> (ø)
storage/myisammrg/myrg_write.c	0.00% <0.00%> (ø)
...y/strategies/agnostic/simplify_douglas_peucker.hpp	0.00% <0.00%> (ø)
sql/rpl_utility.cc	17.17% <0.00%> (ø)
... and 1798 more

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[lujiashun]

LGTM