Revert "Allow specifying the source of the column by overriding columns with aliased columns"

After some thought it was probably not the brightest idea, because it breaks
perfectly valid SQL queries, like SELECTing the same column twice. The projection
mapping issue should be solved in a better way.

This reverts commit ec2f0d62ae6a825d8e30efd15b170fa7156756d7.

Conflicts:
	library/src/main/java/com/getbase/android/db/query/Query.java
	library/src/test/java/com/getbase/android/db/query/QueryTest.java