Remove the soft component sources from libstagefright_omx

These were left in because some vendor libs link to
libstagefright_omx for soft component base. Vendor
code now switched to link to libstagefright_omx_soft.

bug: 129272021
test: elfin-userdebug builds
Change-Id: Iee4f77f98c92f1a21fec0e2c351a7d4be3942d4b