bpmodify: Don't add newlines when removing.

Removing strings and properties currently leaves behind an extra
blank line, because the next value's position causes the printer
to append two newlines instead of one.

To fix this issue, instead of entirely removing the node from
the AST, leave it in place, but mark it as deleted. When printing
a deleted value, advance the position as if the value was printed,
but do not actually print anything.

Bug: 444266638
Test: modify unit test not to ignore newlines and add test case
Flag: EXEMPT HOST_MODE
Change-Id: I7871a6919d59a53468442ec79a7290eb4a728612