Remove the count variable from bazel#Execute

problem: E46: Cannot change read-only variable "count"
solution: Remove the count variable

By default using "let var = value" tries to set the internal
variable var. To set the local variable, l: prefix should be
used i.e. "let l:var = value".

This issue only affected vim and not neovim.

Closes #4

autoload/bazel.vim

@@ -92,16 +92,15 @@ function! bazel#Execute(action, ...) abort
   let targets = []
 
   let i = 0
-  let count = len(a:000)
 
   " Add all arguments that start with "--" to flags
-  while i < count && a:000[i] =~ "^--."
+  while i < a:0 && a:000[i] =~ "^--."
     call add(flags, a:000[i])
     let i = i + 1
   endwhile
 
   " Add everything until we find "--" to targets
-  while i < count && a:000[i] !~ "^--"
+  while i < a:0 && a:000[i] !~ "^--"
     call add(targets, a:000[i])
     let i = i + 1
   endwhile