pgsql: Remove new XML test cases added by e7192486d.

Remove new XML test cases added by e7192486d.

These turn out to produce libxml2-version-dependent error reports.
They aren't adding value that would justify dealing with that,
so just remove them again.  (I had in fact guessed wrong about
what versions matching xml_2.out would produce, but it doesn't
matter because there are other discrepancies.)

Per buildfarm.

Discussion: https://postgr.es/m/trinity-b0161630-d230-4598-9ebc-7a23acdb37cb-1720186432160@3c-app-gmx-bap25
Discussion: https://postgr.es/m/trinity-361ba18b-541a-4fe7-bc63-655ae3a7d599-1720259822452@3c-app-gmx-bs01

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/896cd266fd34c2dfbf06297b9f2ea89ae8e5a0b1

Modified Files
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src/test/regress/expected/xml.out   | 26 --------------------------
src/test/regress/expected/xml_1.out | 12 ------------
src/test/regress/expected/xml_2.out | 26 --------------------------
src/test/regress/sql/xml.sql        |  4 ----
4 files changed, 68 deletions(-)