src/poky:gawk: Remove References to /usr/local/bin/gawk

Also replace the hashbangs using /bin/gawk to use
${bindir}/gawk

This fixes issues such as
riscv/meta-riscv#384

(From OE-Core rev: 9f58ad97f6587322b716de1c9dc409bb4e1376f0)

Signed-off-by: Khem Raj <raj.khemgmail.com>
Signed-off-by: Richard Purdie <richard.purdielinuxfoundation.org>