Update bzl style, local variables don't start with underscore
The underscore prefix is meaningful only for global variables (to make them package private).
RELNOTES: None.
@@ -17,7 +17,7 @@ title: Style guide for bzl files
* Variables and function names use lowercase with words separated by underscores
(`[a-z][a-z0-9_]*`), e.g. `cc_library`. Top-level private values start with
one underscore. Bazel enforces that private values cannot be used from other
- files.
+ files. Local variables should not use the underscore prefix.
* As in BUILD files, there is no strict line length limit as labels can be long.
When possible, try to use at most 79 characters per line.
