android: Make dex_action.gypi not call md5sum.

No intended behavior change.

dex_action.gypi didn't pass its input_paths variable to dex.py,
but that was only set in a single place, and only to a single file there.
It was only used in java_apk.gypi which does manual threading of
stamp files to order actions (since it's a gypi, it can't easily use type
none targets with dependencies). Since dex.py doesn't look at this
stamp file at all, it doesn't need to rerun when the stamp file disappears.

To make this a bit more obvious, remove dex_action.gypi's input_paths
variable and set 'inputs' directly in the one place with the stamp file.
(dex.py will still rerun if the name of the stamp file changes, due to
regular timestamp handling.)

java_apk.gypi used to set input_paths to two files in proguard-enabled
files – change it to depend only on obfuscate_stamp in proguard builds,
as the step that writes that already depends on instr_stamp. (This isn't
necessary as the proguard state is part of the dex.py commandline, so
toggling between proguard and no proguard would rebuild correctly
anyways, but it's conceptually a bit nicer.)

Also set proguard_enabled_input_path unconditionally. Again, no behavior
change, but keeps the gyp a bit shorter.

BUG=177552
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=255325

R=cjhopman@chromium.org

Review URL: https://codereview.chromium.org/183883024

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255403 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255403