Revert r254031: "ELF2: LinkerScript: lookup absolute paths under sysroot"

The test fails on Windows:

Command 34: "ld.lld" "-o" "D:\src\llvm\build.release\tools\lld\test\ELF\Output\l
inkerscript.s.tmp2" "D:\src\llvm\build.release\tools\lld\test\ELF\Output\linkers
cript.s.tmp.dir/xyz.script" "--sysroot=D:\src\llvm\build.release\tools\lld\test\
ELF\Output\linkerscript.s.tmp.dir"
Command 34 Result: 1
Command 34 Output:

Command 34 Stderr:
Unable to find /libxyz.a

llvm-svn: 254049