Remove shard targeted keyspace from database qualifier on the query

[harshit-gangal]

Description

This PR handles the case where database qualifier is removed before sending the query down to vttablet for shard targeted queries.
It only removed the qualifier that matches the targeted keyspace.

Example:

use ks/80-;
select 1 from ks1.t1 join vt_ks1.t2 join information_schema.tables

Query send down to shard 80- will be
select 1 from t1 join vt_ks1.t2 join information_schema.tables

Related Issue(s)

• Closes Bug Report: Specifying database name in a query after shard targetting fails #17502

Checklist

• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.72%. Comparing base (694b02c) to head (a2e93cf).
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17503      +/-   ##
==========================================
+ Coverage   67.68%   67.72%   +0.03%     
==========================================
  Files        1584     1584              
  Lines      254505   254502       -3     
==========================================
+ Hits       172255   172353      +98     
+ Misses      82250    82149     -101     

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[systay]

no need to replace here. it's just writing in the expression we already had there

[harshit-gangal]

I tried the change and it fails.
TableName is not used by reference so I believe we have to do the replace.

[harshit-gangal]

I refactored the methods as there were 3 functions which similar code.