parisc: remove check for minimum required GCC version

Commit cafa0010 ("Raise the minimum required gcc version to 4.6")
bumped the minimum GCC version to 4.6 for all architectures.

The version check in arch/parisc/Makefile is obsolete now.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Helge Deller <deller@gmx.de>