Remove BS4 helpers on response and add WagtailTestUtils.get_soup #118

Job	Run time
test-postgres (3.8, Django>=3.2,<3.3, false, --parallel)	12m 7s
test-postgres (3.11, Django>=4.2,<4.3, postgres:12, notz, false, --parallel)	13m 32s
test-postgres (3.10, Django>=4.1,<4.2, false, emailuser, --parallel)	9m 27s
test-postgres (3.10, git+https://github.com/django/django.git@stable/4.2.x#egg=Django, true, post...	17m 0s
test-postgres (3.10, git+https://github.com/django/django.git@main#egg=Django, true, postgres:12,...	11m 36s
test-postgres-elasticsearch7 (3.8, Django>=4.1,<4.2, false)	8m 17s
test-postgres-elasticsearch6 (3.8, Django>=3.2,<3.3)	8m 51s
test-mysql (3.8, Django>=3.2,<3.3, false)	18m 13s
test-mysql (3.10, Django>=4.2,<4.3, false, --parallel)	18m 14s
test-sqlite (3.9, Django>=4.1,<4.2)	14m 45s
test-sqlite-elasticsearch5 (3.8, Django>=3.2,<3.3)	7m 39s
test-sqlite-elasticsearch8 (3.10, Django>=4.2,<4.3, emailuser)	7m 48s
coverage	1s
	2h 27m 30s

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