gitweb: Remove function prototypes (cleanup)

Use of function prototypes is considered bad practice in Perl.  The
ones used here didn't accomplish anything anyhow, so they've been
removed.

>From perlsub(1):

  [...] the intent of this feature [prototypes] is primarily to let
  you define subroutines that work like built-in functions [...]
  you can generate new syntax with it [...]

We don't want to have subroutines behaving exactly like built-in
functions, we don't want to define new syntax / syntactic sugar, so
prototypes in gitweb are not needed... and they can have unintended
consequences.

Signed-off-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>