Remove ld.config.txt from sdkext APEX

Dynamic linker will use generated linker configuration in general. As
ld.config.txt file in the APEX module will not be used, we can remove
this to avoid confusion.

Bug: 149887007
Test: m -j passed
Test: Boot succeeded from cuttlefish and walleye
Change-Id: I10466863faed3463c69aaec7649f1a5f25b62f17