[gdb/testsuite] Use main.c in gdb.dwarf2

[gdb/testsuite] Use main.c in gdb.dwarf2

Eliminate copies of main.c in gdb.dwarf2.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-10-20  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/arr-stride.c: Remove.
	* gdb.dwarf2/arr-stride.exp: Use main.c.
	* gdb.dwarf2/arr-subrange.c: Remove.
	* gdb.dwarf2/arr-subrange.exp: Use main.c.
	* gdb.dwarf2/bad-regnum.c: Remove.
	* gdb.dwarf2/bad-regnum.exp: Use main.c.
	* gdb.dwarf2/corrupt.c: Remove.
	* gdb.dwarf2/corrupt.exp: Use main.c.
	* gdb.dwarf2/dw2-bad-elf.c: Remove.
	* gdb.dwarf2/dw2-bad-elf.exp: Use main.c.
	* gdb.dwarf2/dw2-icycle.c: Remove.
	* gdb.dwarf2/dw2-icycle.exp: Use main.c.
	* gdb.dwarf2/formdata16.c: Remove.
	* gdb.dwarf2/formdata16.exp: Use main.c.
	* gdb.dwarf2/implptrconst.c: Remove.
	* gdb.dwarf2/implptrconst.exp: Use main.c.
	* gdb.dwarf2/info-locals-optimized-out.c: Remove.
	* gdb.dwarf2/info-locals-optimized-out.exp: Use main.c.
	* gdb.dwarf2/opaque-type-lookup.c: Remove.
	* gdb.dwarf2/opaque-type-lookup.exp: Use main.c.