Cleanup plurals in Settings, change <one> to <1> in string res file.

"One" and "1" are not same, such as "1st place" vs "a
place". Also in many languages, plurals expression is different with English, for more detail please check: go/android-i18n-plurals.
So in string res file, replace "one" with excat value "1" is a more
proper way.

Test: Existing unit tests still pass.
Bug: 199230342
Change-Id: I832abc38afc5d8816fa803865c25e6017cffa2c6