Remove unused Context.ModulePath
Remove unused Context.ModulePath

Context.ModulePath is a duplicate of Context.BlueprintFile, and is
misleading because it returns the path to the Android.bp, and not
the path to the directory that contains the Android.bp file like
ModuleContext.ModuleDir.

Change-Id: I505136fce3c3d37595cd4b4e08de5e2691a2a0f6

google/blueprint,google/blueprint