Revert "[lldb] Use vFlash commands when writing to target's flash memory regions"

This reverts commit r326261 as it introduces inconsistencies in the
handling of load addresses for ObjectFileELF -- some parts of the class
use physical addresses, and some use virtual. This has manifested itself
as us not being able to set the load address of the vdso "module" on
android.

llvm-svn: 326367