composetable: Drop GtkComposeTableCompact

composetable: Drop GtkComposeTableCompact

All tables use the compact format now, and we generate
caches in that format too. Bump the cache version to 3
for this.

Replace the python script for generating the builtin table
by a small C program using the same code to generate the data
for the builtin table. This drops the restriction on only
generating a single character in the builtin sequences.