runtime: don't define libc_getpid in os3_solaris.go

The function is already defined between syscall_solaris.go and
syscall2_solaris.go.

Change-Id: I034baf7c8531566bebfdbc5a4061352cbcc31449
Reviewed-on: https://go-review.googlesource.com/12773Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/os3_solaris.go

@@ -16,7 +16,6 @@ import "unsafe"
 //go:cgo_import_dynamic libc_exit exit "libc.so"
 //go:cgo_import_dynamic libc_fstat fstat "libc.so"
 //go:cgo_import_dynamic libc_getcontext getcontext "libc.so"
-//go:cgo_import_dynamic libc_getpid getpid "libc.so"
 //go:cgo_import_dynamic libc_getrlimit getrlimit "libc.so"
 //go:cgo_import_dynamic libc_kill kill "libc.so"
 //go:cgo_import_dynamic libc_madvise madvise "libc.so"
@@ -52,7 +51,6 @@ import "unsafe"
 //go:linkname libc_exit libc_exit
 //go:linkname libc_fstat libc_fstat
 //go:linkname libc_getcontext libc_getcontext
-//go:linkname libc_getpid libc_getpid
 //go:linkname libc_getrlimit libc_getrlimit
 //go:linkname libc_kill libc_kill
 //go:linkname libc_madvise libc_madvise
@@ -89,7 +87,6 @@ var (
 	libc_exit,
 	libc_fstat,
 	libc_getcontext,
-	libc_getpid,
 	libc_getrlimit,
 	libc_kill,
 	libc_madvise,