glcpp: Delete copies of hash_table.c, hash_table.h, and other headers.

glcpp: Delete copies of hash_table.c, hash_table.h, and other headers.

These were only ever intended to exist in the original, standalone
implementation of glcpp, (with the idea of dropping them as soon as
the code moved into mesa). The current build system wasn't compiling
this C file, but the presence of the header files could cause problems
if the two copies diverge in the future.

We head those problems off by deleting al of these redundant files.