meson: avoid compiling C++ files twice
meson: avoid compiling C++ files twice

The files src/IndelAllele.cpp and src/LeftAlign.cpp were marked as
sources in both of the executables.

The static library corresponds to the 'object library' in CMakeLists.txt:
    add_library(freebayes_OBJS OBJECT ...)

ekg/freebayes,ekg/freebayes,ekg/freebayes,ekg/freebayes,ekg/freebayes