GH-49632: [C++][R] Remove deprecated old MinGW CMake fixes for AWS (#… #6016

Job	Run time
check-labels / Check labels	2s
JNI macOS	18m 17s
JNI ubuntu-latest amd64	18m 13s
JNI ubuntu-24.04-arm arm64v8	18m 12s
ODBC release ARM64 macOS 14	18m 27s
ODBC debug ARM64 macOS 14	18m 13s
ODBC Linux	18m 12s
ODBC debug AMD64 macOS 15-intel	18m 23s
AMD64 Ubuntu Large Memory Tests	17m 50s
AMD64 Ubuntu Meson	18m 12s
ODBC Windows	18m 13s
AMD64 Alpine Linux	18m 12s
ARM64 Windows 11 MSVC / windows	18m 20s
ODBC release AMD64 macOS 15-intel	18m 25s
AMD64 Debian C++23	15m 57s
ODBC nightly	1s
ODBC release	1s
report-extra-cpp	0s
	4h 13m 10s

Provide feedback