unifdef looks promising.
The current unifdef-2.6 does not process the #defines included from types.h, so for the trivial command unifdef types.c -o output.txt, the output is unchanged.
Using the brain to parse types.h, one can define ALPHA, BETA, and GAMMA via the command line: unifdef -DALPHA=1 -DBETA -DGAMMA=0 types.c -o output.txt, but unfortunately, this removes all preprocessor commands, not only the GAMMA commands.
So, to get rid of only the GAMMA commands, one has to define only GAMMA on the command line: unifdef -DGAMMA=0 types.c -o output.txt. This gives the expected result.
unifdef seems to completely ignore #include and #define. So, types.h is not read at all, and even if it would be read, the #defines have no effect.
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)