Disable IsPage till perf regression is fixed

[atiq-cs]

Reverse commit 8c248f0 partially ref. #24, rel. #25

For our large blog, build completes within 12 minutes with this change. Without this change, build keep running forever!

[atiq-cs]

@daveaglick @rdeago please have a look.

[daveaglick]

Note: This is related to the discussion in #34 - going to do some work there to try and uncover the source of the slowness before merging this fix, since the code removed here will change the behavior of the theme (specifically, the navbar will show different things before and after the change).

We'll circle back to this PR after trying to get to the bottom of why it's needed in the first place.