android doc browser: let's list file extensions only at a single place

There is still some duplication, as the file type -> resource mapping is
there two times.

Change-Id: I50cd58f1cc62e872fb925556dd151f6392eeeb87
android doc browser: sync file type list with the intent filter

Change-Id: I81746860198864bb5917a6c1e898b742b65d77e1