Merge "Remove the weird range variants of String8::toLower() and...

Merge "Remove the weird range variants of String8::toLower() and String8::toUpper()." am: 561209ee am: 7e7ff363 am: 685c0c9a

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1670567

Change-Id: Iedb8ab438496e0fa3f6697fb18b060e3a1acbc89