Fix The GNU ToolChain Authors copyright notice

I (and maybe one or two others) added a (C) to the copyright notice
regardless of the contribution checklist[1] not mentioning it.  Fix all
these instances so that the notice reads as "Copyright The GNU Toolchain
Authors" across the source code.

[1] https://sourceware.org/glibc/wiki/Contribution%20checklist



Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>