Revert test case added by commit 1e165d05fe.

The buildfarm is still showing at least three distinct behaviors for
a bad locale name in CREATE COLLATION.  Although this test was helpful
for getting the error reporting code into some usable shape, it doesn't
seem worth carrying multiple expected-files in order to support the
test in perpetuity.  So pull it back out.

Discussion: https://postgr.es/m/CAKKotZS-wcDcofXDCH=sidiuajE+nqHn2CGjLLX78anyDmi3gQ@mail.gmail.com

src/test/regress/expected/collate.out

@@ -627,9 +627,6 @@ CREATE COLLATION mycoll1 FROM "C";
 CREATE COLLATION mycoll2 ( LC_COLLATE = "POSIX", LC_CTYPE = "POSIX" );
 CREATE COLLATION mycoll3 FROM "default";  -- intentionally unsupported
 ERROR:  collation "default" cannot be copied
-CREATE COLLATION mycoll4 ( LOCALE = "no_such_locale" );  -- fail
-ERROR:  could not create locale "no_such_locale": No such file or directory
-DETAIL:  The operating system could not find any locale data for the locale name "no_such_locale".
 DROP COLLATION mycoll1;
 CREATE TABLE collate_test23 (f1 text collate mycoll2);
 DROP COLLATION mycoll2;  -- fail

src/test/regress/sql/collate.sql

@@ -234,7 +234,6 @@ EXPLAIN (COSTS OFF)
 CREATE COLLATION mycoll1 FROM "C";
 CREATE COLLATION mycoll2 ( LC_COLLATE = "POSIX", LC_CTYPE = "POSIX" );
 CREATE COLLATION mycoll3 FROM "default";  -- intentionally unsupported
-CREATE COLLATION mycoll4 ( LOCALE = "no_such_locale" );  -- fail
 
 DROP COLLATION mycoll1;
 CREATE TABLE collate_test23 (f1 text collate mycoll2);