packagegroup-core-tools-testapps: clear GOTOOLS for riscv32

go-helloworld is not compatible with riscv32 and causes error:

| ERROR: Nothing RPROVIDES 'go-helloworld' (but
    meta/recipes-core/packagegroups/packagegroup-core-tools-testapps.bb
    RDEPENDS on or otherwise requires it)
| go-helloworld was skipped: Unsupported CPU architecture: riscv32

Clear GOTOOLS for riscv32 in recipe packagegroup-core-tools-testapps.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>