tests: Remove unnecessary port config with VanillaPostgres class

VanillaPostgres constructor prints the "port={port}" line to the
config file, no need to do it in the callers.

The TODO comment that it would be nice if VanillaPostgres could pick
the port by itself is still valid though.

test_runner/fixtures/neon_fixtures.py

@@ -2458,6 +2458,7 @@ def pg_bin(test_output_dir: Path, pg_distrib_dir: Path, pg_version: PgVersion) -
     return PgBin(test_output_dir, pg_distrib_dir, pg_version)
 
 
+# TODO make port an optional argument
 class VanillaPostgres(PgProtocol):
     def __init__(self, pgdatadir: Path, pg_bin: PgBin, port: int, init: bool = True):
         super().__init__(host="localhost", port=port, dbname="postgres")

test_runner/regress/test_fullbackup.py

@@ -66,12 +66,6 @@ def test_fullbackup(
     # Restore from the backup and find the data we inserted
     port = port_distributor.get_port()
     with VanillaPostgres(restored_dir_path, pg_bin, port, init=False) as vanilla_pg:
-        # TODO make port an optional argument
-        vanilla_pg.configure(
-            [
-                f"port={port}",
-            ]
-        )
         vanilla_pg.start()
         num_rows_found = vanilla_pg.safe_psql("select count(*) from tbl;", user="cloud_admin")[0][0]
         assert num_rows == num_rows_found

test_runner/regress/test_timeline_size.py

@@ -579,7 +579,6 @@ def test_timeline_size_metrics(
     pg_bin = PgBin(test_output_dir, pg_distrib_dir, pg_version)
     port = port_distributor.get_port()
     with VanillaPostgres(pgdatadir, pg_bin, port) as vanilla_pg:
-        vanilla_pg.configure([f"port={port}"])
         vanilla_pg.start()
 
         # Create database based on template0 because we can't connect to template0