Remove Keymaster::isSecure() and simplify callers

Now that isSecure() always returns true, we can remove it and simplify
all the callers (i.e. cryptfs). Refer to the commit description for
Iaebfef082eca0da8a305043fafb6d85e5de14cf8 for why this function always
return true.

Bug: 181910578
Test: Cuttlefish and bramble boot
Change-Id: I185dd8180bd7842b05295263f0b1aa7205329a88
3 files changed