Revert "Reduce number of allocation when writing string vec"

This reverts commit 9f16bc66.

Reason for revert: trusty_test_xts builds are broken during a test due to implicit conversion:
[   67.594669][   T81] trusty-log trusty-ffa:trusty-core:log: UBSan: (implicit conversion) frameworks/native/libs/binder/include/binder/Parcel.h:1103:56
[   67.595565][   T81] trusty-log trusty-ffa:trusty-core:log: Details: implicit conversion (sign change) from -4 to 18446744073709551612

Bug: 438750707
Change-Id: Ibbe72c431969c63552a180aa7d7b300ab839b0ae