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

Deployment Notes

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[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.69%. Comparing base (694b02c) to head (b4b88ee).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/sqlparser/ast_funcs.go	85.71%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17503      +/-   ##
==========================================
+ Coverage   67.68%   67.69%   +0.01%     
==========================================
  Files        1584     1584              
  Lines      254505   254512       +7     
==========================================
+ Hits       172255   172290      +35     
+ Misses      82250    82222      -28     

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