chore(docs): Remove entries for two known limitations which were fixed recently

[martin-g]

Which issue does this PR close?

N/A

Rationale for this change

Two known limitations have been fixed recently, so there is no need to list them anymore in the DML Known limitations section

1. Issue: A DELETE or an UPDATE with an IN or an EXISTS subquery in its WHERE clause changes every row #24654, PR: fix(core): reject a DELETE or an UPDATE whose WHERE clause cannot reach the provider #24657
2. Issue: EXPLAIN DELETE and EXPLAIN UPDATE execute the statement on an in-memory table #24656, PR: fix: apply MemTable DELETE and UPDATE at execution, not planning #25040

What changes are included in this PR?

Remove the entries from user-guide/sql/dml.md

What is the testing strategy for this PR?

Build the docs and verify that the obsolete entries are no more there.

Are there any user-facing changes?

No.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.72%. Comparing base (b7c7bc2) to head (07418bf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26113      +/-   ##
==========================================
- Coverage   82.73%   82.72%   -0.01%     
==========================================
  Files        1147     1147              
  Lines      449213   449213              
  Branches   449213   449213              
==========================================
- Hits       371634   371624      -10     
- Misses      54929    54938       +9     
- Partials    22650    22651       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[alamb]

🚀