chore(firestore): remove redundant files #19071

Job	Run time
owlbot-py	1m 15s
generate-readme	1m 12s
group_id_check_for_maps_libraries	8m 49s
root-pom	1m 44s
gitignore_correctness	54s
package_name_check	1m 5s
owlbot-yaml	1m 10s
gapic-bom	1m 36s
	17m 45s

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