PR23611, objcopy is not removing executable relocatable sections

PR23611, objcopy is not removing executable relocatable sections

BFD handles ELF relocation sections in an executable differently to
relocation sections in a relocatable object.  For a relocatable
object, BFD carries the relocations as data associated with the
section to which they apply; The relocation section doesn't appear as
a separate section.  For an executable, dynamic relocation sections do
appear as separate sections.  This means that objcopy needs to use
different strategies when dealing with relocations.

When --remove-relocations was added to objcopy with commit
d3e5f6c8f1e, objcopy lost the ability to remove dynamic relocation
sections such as .rela.plt from executables using the option
"--remove-section=.rela.plt".  This patch reinstates that
functionality.

I thought it best to keep --remove-relocations as is, rather than
extending to handle dynamic relocations as per the patch in the PR,
because executables linked with --emit-relocs may have both dynamic
and non-dynamic relocations.  In that case --remove-relocataions=* is
useful to remove all the non-dynamic relocations.

	PR binutils/23611
	* objcopy.c (handle_remove_section_option): Consider .rela and
	.rel sections for stripping directly as well as attached to the
	associated section they relocate.
	* doc/binutils.texi (remove-relocations): Specify that this
	option removes non-dynamic relocation sections.
	* testsuite/binutils-all/objcopy.exp
	(objcopy_remove_relocations_from_executable): New test.