Remove String8(StaticLinkage) references.

These are a legacy holdover from when libutils String8 couldn't be used
at static time.

Bug: 150325737 # fixing GSI breakage
Test: N/A
Change-Id: I009b2ca53631509072b4085f3f53c0b94e71b13e
(cherry picked from commit 15f04b8a)
Merged-In: I009b2ca53631509072b4085f3f53c0b94e71b13e